docs: fix typo on credentials_info usage sample (#1145)

fix typo on credentials_info usage sample

Author: yugoccp

README.rst

@@ -136,7 +136,7 @@ Alternatively, you can choose either of the following approaches:
     credentials_info = {
         "type": "service_account", 
         "project_id": "your-service-account-project-id"
-    },
+    }
     engine = create_engine('bigquery://', credentials_info=credentials_info)
 
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