I did that and it worked but only for 10 seconds! I don't know how could the world be from 1.13 and the server 1.12.2 because I play it for almost a year and it worked just fine.
Anyways I will try to change server version and if that doesn't work too I will make a new world
CONSOLE==================================================================================
1[18:27:49] [Server thread/INFO]: Starting minecraft server version 1.12.2
2[18:27:49] [Server thread/INFO]: Loading properties
3[18:27:49] [Server thread/INFO]: Default game type: SURVIVAL
4[18:27:49] [Server thread/INFO]: Generating keypair
5[18:27:50] [Server thread/INFO]: Starting Minecraft server on *:10107
6[18:27:50] [Server thread/INFO]: Using epoll channel type
7[18:27:51] [Server thread/INFO]: This server is running CraftBukkit version git-Bukkit-2b93d83 (MC: 1.12.2) (Implementing API version 1.12.2-R0.1-SNAPSHOT)
8[18:27:52] [Server thread/INFO]: [Spawner] Loading Spawner v2.8.3-1603e95
9[18:27:52] [Server thread/WARN]: **** SERVER IS RUNNING IN OFFLINE/INSECURE MODE!
10[18:27:52] [Server thread/WARN]: The server will make no attempt to authenticate usernames. Beware.
11[18:27:52] [Server thread/WARN]: While this makes the game possible to play without internet access, it also opens up the ability for hackers to connect with any username they choose.
12[18:27:52] [Server thread/WARN]: To change this, set "online-mode" to "true" in the server.properties file.
13[18:27:52] [Server thread/INFO]: Preparing level "world"
14[18:27:55] [Server thread/INFO]: Preparing start region for level 0 (Seed: -3132471201760488043)
15[18:27:58] [Server thread/INFO]: Preparing spawn area: 0%
16[18:27:59] [Server thread/INFO]: Preparing spawn area: 6%
17[18:28:00] [Server thread/INFO]: Preparing spawn area: 46%
18[18:28:01] [Server thread/INFO]: Preparing spawn area: 75%
19[18:28:02] [Server thread/INFO]: Preparing start region for level 1 (Seed: -8901568246881463268)
20[18:28:03] [Server thread/INFO]: Preparing spawn area: 2%
21[18:28:04] [Server thread/INFO]: Preparing spawn area: 4%
22[18:28:05] [Server thread/INFO]: Preparing spawn area: 7%
23[18:28:06] [Server thread/INFO]: Preparing spawn area: 10%
24[18:28:07] [Server thread/INFO]: Preparing spawn area: 13%
25[18:28:09] [Server thread/INFO]: Preparing spawn area: 15%
26[18:28:10] [Server thread/INFO]: Preparing spawn area: 19%
27[18:28:11] [Server thread/INFO]: Preparing spawn area: 23%
28[18:28:12] [Server thread/INFO]: Preparing spawn area: 29%
29[18:28:13] [Server thread/INFO]: Preparing spawn area: 38%
30[18:28:14] [Server thread/INFO]: Preparing spawn area: 43%
31[18:28:15] [Server thread/INFO]: Preparing spawn area: 52%
32[18:28:16] [Server thread/INFO]: Preparing spawn area: 62%
33[18:28:17] [Server thread/INFO]: Preparing spawn area: 71%
34[18:28:18] [Server thread/INFO]: Preparing spawn area: 79%
35[18:28:19] [Server thread/INFO]: Preparing spawn area: 84%
36[18:28:20] [Server thread/INFO]: Preparing spawn area: 90%
37[18:28:21] [Server thread/INFO]: Preparing start region for level 2 (Seed: -8901568246881463268)
38[18:28:22] [Server thread/INFO]: Preparing spawn area: 12%
39[18:28:23] [Server thread/INFO]: Preparing spawn area: 30%
40[18:28:24] [Server thread/INFO]: Preparing spawn area: 40%
41[18:28:26] [Server thread/INFO]: Preparing spawn area: 43%
42[18:28:27] [Server thread/INFO]: Preparing spawn area: 57%
43[18:28:28] [Server thread/INFO]: Preparing spawn area: 74%
44[18:28:29] [Server thread/INFO]: Preparing spawn area: 89%
45[18:28:29] [Server thread/INFO]: [Spawner] Enabling Spawner v2.8.3-1603e95
46[18:28:29] [Server thread/INFO]: [Spawner] Loading support for v1_12_R1
47[18:28:29] [Server thread/ERROR]: [Spawner] Plugin Spawner v2.8.3-1603e95 has failed to register events for class me.ryvix.spawner.SpawnerEvents because org/bukkit/event/entity/SpawnerSpawnEvent does not exist.
48[18:28:29] [Server thread/INFO]: Server permissions file permissions.yml is empty, ignoring it
49[18:28:29] [Server thread/INFO]: Done (37.138s)! For help, type "help" or "?"
50[18:28:29] [Server thread/INFO]: Starting GS4 status listener
51[18:28:29] [Query Listener #1/INFO]: Query running on **.**.**.**:10107
52[18:28:34] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 4113ms behind, skipping 82 tick(s)
53[18:29:01] [Server thread/INFO]: Opped Koljo99
54[18:32:13] [Server thread/INFO]: Koljo99[/**.**.**.**:53660] logged in with entity id 211 at ([world]108.5, 64.0, -248.5)
55[18:32:31] [Server thread/INFO]: Koljo99 issued server command: /gamemode 1
56[18:32:31] [Server thread/INFO]: [Koljo99: Set own game mode to Creative Mode]
57[18:32:42] [Chunk I/O Executor Thread-1/WARN]: Could not set level chunk heightmap, array length is 0 instead of 256
58[18:32:42] [Server thread/ERROR]: Encountered an unexpected exception
59java.lang.IllegalArgumentException: ChunkNibbleArrays should be 2048 bytes not: 0
60 at net.minecraft.server.v1_12_R1.NibbleArray.<init>(SourceFile:16) ~[minecraft_server.jar:git-Bukkit-2b93d83]
61 at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:374) ~[minecraft_server.jar:git-Bukkit-2b93d83]
62 at net.minecraft.server.v1_12_R1.ChunkRegionLoader.a(ChunkRegionLoader.java:87) ~[minecraft_server.jar:git-Bukkit-2b93d83]
63 at net.minecraft.server.v1_12_R1.ChunkRegionLoader.loadChunk(ChunkRegionLoader.java:65) ~[minecraft_server.jar:git-Bukkit-2b93d83]
64 at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:21) ~[minecraft_server.jar:git-Bukkit-2b93d83]
65 at org.bukkit.craftbukkit.v1_12_R1.chunkio.ChunkIOProvider.callStage1(ChunkIOProvider.java:1) ~[minecraft_server.jar:git-Bukkit-2b93d83]
66 at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.init(AsynchronousExecutor.java:150) ~[minecraft_server.jar:git-Bukkit-2b93d83]
67 at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.initAsync(AsynchronousExecutor.java:95) ~[minecraft_server.jar:git-Bukkit-2b93d83]
68 at org.bukkit.craftbukkit.v1_12_R1.util.AsynchronousExecutor$Task.run(AsynchronousExecutor.java:85) ~[minecraft_server.jar:git-Bukkit-2b93d83]
69 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) ~[?:1.8.0_144]
70 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) ~[?:1.8.0_144]
71 at java.lang.Thread.run(Thread.java:748) [?:1.8.0_144]
72[18:32:43] [Server thread/ERROR]: This crash report has been saved to: /aternos/server/./crash-reports/crash-2019-01-15_18.32.42-server.txt
73[18:32:43] [Server thread/INFO]: Stopping server
74[18:32:43] [Server thread/INFO]: [Spawner] Disabling Spawner v2.8.3-1603e95
75[18:32:43] [Server thread/INFO]: Saving players
76[18:32:43] [Server thread/INFO]: Koljo99 lost connection: Server closed
77[18:32:43] [Server thread/INFO]: Koljo99 left the game
78[18:32:43] [Server thread/INFO]: Saving worlds
79[18:32:43] [Server thread/INFO]: Saving chunks for level 'world'/overworld
80[18:32:44] [Server thread/INFO]: Saving chunks for level 'world_nether'/the_nether
81[18:32:44] [Server thread/INFO]: Saving chunks for level 'world_the_end'/the_end