trailing commas on dicts

Author: rgbkrk

docs/messaging.rst

@@ -965,11 +965,11 @@ Message type: ``display_data``::
         'data' : dict,
 
         # Any metadata that describes the data
-        'metadata' : dict
+        'metadata' : dict,
 
         # Optional transient data. Information not to be persisted to a notebook
         # or other documents. Intended to live only during a live kernel session.
-        'transient': dict
+        'transient': dict,
     }
 
 
@@ -1034,11 +1034,11 @@ Message type: ``update_display_data``::
         'data' : dict,
 
         # Any metadata that describes the data
-        'metadata' : dict
+        'metadata' : dict,
 
         # Any information not to be persisted to a notebook or other environment
         # Intended to live only during a kernel session
-        'transient': dict
+        'transient': dict,
     }
 
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