Add blank line in utils.py

Author: petahz

cache_helper/utils.py

@@ -156,4 +156,4 @@ def _plumb_collections(input_item):
     # trim trailing comma
     return_string = ''.join(return_list)
     # trim last ',' because it lacks significant meaning.
-    return return_string[:-1]
+    return return_string[:-1]