Synchronize on the class instead of the instance

I didn't realize it before, but it looks like there is at least one instance of YamlRegionFile per world, so synchronizing on the instance wouldn't necessarily help.

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

@@ -192,9 +192,10 @@ public class YamlRegionFile implements RegionDatabase {
     }
 
     @Override
-    public synchronized void saveAll(Set<ProtectedRegion> regions) throws StorageException {
+    public void saveAll(Set<ProtectedRegion> regions) throws StorageException {
         checkNotNull(regions);
 
+        synchronized (YamlRegionFile.class) {
             File tempFile = new File(file.getParentFile(), file.getName() + ".tmp");
             YAMLProcessor config = createYamlProcessor(tempFile);
 
@@ -254,6 +255,7 @@ public class YamlRegionFile implements RegionDatabase {
                 throw new StorageException("Failed to rename temporary regions file to " + file.getAbsolutePath());
             }
         }
+    }
 
     @Override
     public void saveChanges(RegionDifference difference) throws DifferenceSaveException {