Synchronize YamlRegionFile#saveAll

This prevents multiple invocations of the method from intersecting, which could potentially cause the .tmp file to be overwritten before being renamed, thus corrupting the region storage

worldguard-core/src/main/java/com/sk89q/worldguard/protection/managers/storage/file/YamlRegionFile.java

@@ -192,7 +192,7 @@ public Set<ProtectedRegion> loadAll(FlagRegistry flagRegistry) throws StorageExc
     }
 
     @Override
-    public void saveAll(Set<ProtectedRegion> regions) throws StorageException {
+    public synchronized void saveAll(Set<ProtectedRegion> regions) throws StorageException {
         checkNotNull(regions);
 
         File tempFile = new File(file.getParentFile(), file.getName() + ".tmp");