Fix exception handle while decoding JSON message

This was meant to handle simplejson's exception class but it makes no
sense if it's inheriting from ValueError and would raise an exception
if simplejson is not installed which is not acceptable. See #16.

Author: EvaSDK

fluent/handler.py

@@ -50,7 +50,7 @@ def _structuring(self, data, msg):
         elif isinstance(msg, basestring):
             try:
                 self._add_dic(data, json.loads(str(msg)))
-            except (ValueError, json.JSONDecodeError):
+            except ValueError:
                 self._add_dic(data, {'message': msg})
 
     @staticmethod