Fix chunk y position

src/main/java/com/moulberry/axiom/packet/ChunkSectionModifier.java

@@ -56,7 +56,7 @@ public class ChunkSectionModifier {
         lightEngine = getLightEngine.invoke(chunkSource);
         chunk = AxiomPaper.getChunk(level, cx, cz);
 
-        section = getSection.invoke(chunk, cy + world.getMinHeight() / 16);
+        section = getSection.invoke(chunk, cy - world.getMinHeight() / 16);
         hadOnlyAir = hasOnlyAir.invoke(section);
 
         heightmaps = types.stream().map(chunkHeightmaps.get(chunk)::get).toArray(Heightmap[]::new);