kafka.py: fix producer setting max.request.size -> message.max.bytes to match librdkafka config

ligo/scald/io/kafka.py

@@ -39,7 +39,7 @@ class Client(object):
             'group.id': self.uri.groupid,
         }
         self._producer_settings = {
-            'max.request.size': 5242880,  # 5 MB
+            'message.max.bytes': 5242880,  # 5 MB
             **self._kafka_settings,
         }