Fix non ascii character bug

If file contains non-ascii characters then PandocRender fails with exception:
Writing file ... with encoding UTF-8
Traceback (most recent call last):
  File "./sublime_plugin.py", line 356, in run_
  File "./PandocRender.py", line 42, in run
UnicodeEncodeError: 'ascii' codec can't encode characters in position 29-33: ordinal not in range(128)