Fix example for confluentinc#1078 (confluentinc#1282, @rmoff)

The argument order in the constructor signature for AvroSerializer
was altered in v1.6.1, but the example is not changed yet.

Author: rmoff

examples/avro_producer.py

@@ -115,8 +115,8 @@ def main(args):
     schema_registry_conf = {'url': args.schema_registry}
     schema_registry_client = SchemaRegistryClient(schema_registry_conf)
 
-    avro_serializer = AvroSerializer(schema_str,
-                                     schema_registry_client,
+    avro_serializer = AvroSerializer(schema_registry_client,
+                                     schema_str,
                                      user_to_dict)
 
     producer_conf = {'bootstrap.servers': args.bootstrap_servers,