fix problem with files contains utf-8 symbols

Fix this error:

File "./beautify_ruby.py", line 37, in beautify_buffer
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 671, in communicate
    return self._communicate(input)

UnicodeEncodeError: 'ascii' codec can't encode character u'\u0432' in position 395: ordinal not in range(128)