Fix Custom Logic Adds Field test for Python 2.6

The Formatter class in the logging package of Python 2.6 is old style.

To be able to still run the test on Python 2.6, this needs to be the
old style "super".

Author: nelsonjchen

tests/tests.py

@@ -147,7 +147,9 @@ class CustomJsonFormatter(jsonlogger.JsonFormatter):
 
             def process_log_record(self, log_record):
                 log_record["custom"] = "value"
-                return super(CustomJsonFormatter, self).process_log_record(log_record)
+                # Old Style "super" since Python 2.6's logging.Formatter is old
+                # style
+                return jsonlogger.JsonFormatter.process_log_record(self, log_record)
 
         self.logHandler.setFormatter(CustomJsonFormatter())
         self.logger.info("message")