title: Vim Flake8 ignoring project config file
body: <p>vim-flake8 seems to be ignoring my project-specific config file.  If I run flake8 from the command line in my project root, it works, but when I open vim and try to run flake8 against my files, its not picking up that setting.  I know this because its using a default line-length of 79, instead of my project-specific 120.</p>
  
  <p>I read this post: <a href="https://stackoverflow.com/questions/28436382/flake8-not-picking-up-config-file">flake8 not picking up config file</a>, but it doesn't seem to help.  It mentions a bug fixed over a year ago in the comments.</p>
  
  <p>In my project root, I have a <code>.flake8</code> file with a <code>[flake8]</code> section.  </p>
  
  <p>How does vim-flake8 determine what the project root is and where to look for the config file?  Does it just use the directory in which Vim is opened?</p>