UnicodeEncodeError: bumpversion -h | grep part

[peritus]

Originally reported by @jalanb in #11

$ bumpversion -h | grep part
Traceback (most recent call last):
  File "/Users/jab/bin/bumpversion", line 7, in <module>
    main()
  File "/usr/local/lib/python2.7/site-packages/bumpversion/__init__.py", line 301, in main
    args = parser3.parse_args(remaining_argv)
  File "/usr/local/lib/python2.7/argparse.py", line 1678, in parse_args
    args, argv = self.parse_known_args(args, namespace)
  File "/usr/local/lib/python2.7/argparse.py", line 1710, in parse_known_args
    namespace, args = self._parse_known_args(args, namespace)
  File "/usr/local/lib/python2.7/argparse.py", line 1916, in _parse_known_args
    start_index = consume_optional(start_index)
  File "/usr/local/lib/python2.7/argparse.py", line 1856, in consume_optional
    take_action(action, args, option_string)
  File "/usr/local/lib/python2.7/argparse.py", line 1784, in take_action
    action(self, namespace, argument_values, option_string)
  File "/usr/local/lib/python2.7/argparse.py", line 993, in __call__
    parser.print_help()
  File "/usr/local/lib/python2.7/argparse.py", line 2303, in print_help
    self._print_message(self.format_help(), file)
  File "/usr/local/lib/python2.7/argparse.py", line 2317, in _print_message
    file.write(message)
UnicodeEncodeError: 'ascii' codec can't encode character u'\u2192' in position 1630: ordinal not in range(128)