remove unnecessary comma

BRONSOLO · BRONSOLO · commit 7f8f68cb6dfd · 2015-06-30T15:04:26.000-04:00
diff --git a/plotly/plotly/plotly.py b/plotly/plotly/plotly.py
@@ -1212,7 +1212,7 @@ def headers(cls):
             headers['authorization'] = 'Basic ' + encoded_proxy_auth
             headers['plotly-authorization'] = 'Basic ' + encoded_api_auth
         else:
-            headers['authorization'] = 'Basic ' + encoded_api_auth,
+            headers['authorization'] = 'Basic ' + encoded_api_auth
 
         return headers
 
