support status code 204

Author: Zhang Qiang

redminelib/engines/base.py

@@ -140,7 +140,7 @@ def process_response(response, return_raw=False):
 
         status_code = response.status_code
 
-        if status_code in (200, 201):
+        if status_code in (200, 201, 204):
             if return_raw:
                 return response
             elif not response.content.strip():