remove .DS_Store if its the only file left

oml/utils.py

@@ -315,6 +315,9 @@ def update_dict(root, data):
 def remove_empty_folders(prefix):
     empty = []
     for root, folders, files in os.walk(prefix):
+        if len(files) == 1 and files[0] == '.DS_Store':
+            os.unlink(os.path.join(root, files[0]))
+            files = []
         if not folders and not files:
             empty.append(root)
     for folder in empty: