Merge branch 'bug/122' into 'master'

Correct usage config_file StyleGuide parameter

Previously, we passed the location for our user config file to the
StyleGuide. This was intended to be a way to tell pep8's StyleGuide
to use that as a user config file, but instead that became the default
for the --config command-line option. This caused that to have higher
priority than the project configuration file.

Closes #122

See merge request !53