title: Error in git checks when running devtools::release() in preparation for releasing package in R
body: <p>I am trying to release a package to CRAN using <code>devtools::release()</code>. Whenever I get to the step for <code>Running Git checks...</code> I get an error. </p>
  
  <pre><code>── Running Git checks for fitzRoy ───────────────────────────────────────────────────────────────────────
  Current branch: master 
  Checking uncommitted files... OK
  Checking synchronisation with remote branch...
  ERROR: Error in 'git2r_remote_fetch': unsupported URL protocol
  </code></pre>
  
  <p>I'm on a Mac. I've been using Git fine for the package and have no dramas committing, pushing and pulling. </p>
  
  <p>I've tried updating devtools, git2r and also installing the latest version of Git but haven't had any luck. </p>
  
  <p>Any suggestions? </p>