In python3 if I do this I get a type error down the line.

"Can't convert 'bytes' object to str implicitly"

```
======================================================================
ERROR: test_mult_inputs_html (diff_cover.tests.test_integration.DiffCoverIntegrationTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/bachmann/Code/diff-cover/diff_cover/tests/test_integration.py", line 220, in test_mult_inputs_html
    ['diff-cover', 'coverage1.xml', 'coverage2.xml']
  File "/Users/bachmann/Code/diff-cover/diff_cover/tests/test_integration.py", line 75, in _check_html_report
    main()
  File "/Users/bachmann/Code/diff-cover/diff_cover/tool.py", line 174, in main
    html_report=arg_dict['html_report'],
  File "/Users/bachmann/Code/diff-cover/diff_cover/tool.py", line 144, in generate_coverage_report
    reporter.generate_report(output_file)
  File "/Users/bachmann/Code/diff-cover/diff_cover/report_generator.py", line 211, in generate_report
    report = template.render(self._context())
  File "/Users/bachmann/Code/diff-cover/diff_cover/report_generator.py", line 236, in _context
    (src, self._src_path_stats(src)) for src in self.src_paths()
  File "/Users/bachmann/Code/diff-cover/diff_cover/report_generator.py", line 82, in src_paths
    return set(src for src, summary in self._diff_violations.items()
  File "/Users/bachmann/Code/diff-cover/.tox/py34/lib/python3.4/site-packages/lazy/lazy.py", line 28, in __get__
    value = self.__func(inst)
  File "/Users/bachmann/Code/diff-cover/diff_cover/report_generator.py", line 175, in _diff_violations
    ) for src_path in self._diff.src_paths_changed()
  File "/Users/bachmann/Code/diff-cover/diff_cover/report_generator.py", line 175, in <genexpr>
    ) for src_path in self._diff.src_paths_changed()
  File "/Users/bachmann/Code/diff-cover/diff_cover/violations_reporter.py", line 173, in violations
    self._cache_file(src_path)
  File "/Users/bachmann/Code/diff-cover/diff_cover/violations_reporter.py", line 134, in _cache_file
    src_path)
  File "/Users/bachmann/Code/diff-cover/diff_cover/violations_reporter.py", line 91, in _get_src_path_line_nodes
    src_rel_path = self._git_path.relative_path(src_path)
  File "/Users/bachmann/Code/diff-cover/diff_cover/git_path.py", line 32, in relative_path
    return os.path.relpath(git_diff_path, root_rel_path)
  File "/Users/bachmann/Code/diff-cover/.tox/py34/bin/../lib/python3.4/posixpath.py", line 449, in relpath
    start_list = [x for x in abspath(start).split(sep) if x]
TypeError: Can't convert 'bytes' object to str implicitly
```