title: Allow travis.ci to push github
body: <p>I was hoping I could just add travis.ci as a collaborator, but didn't find anything in that direction. Maybe it's a security measure because they don't want to leak their credentials in the virtual environment. </p>
  
  <p>Other (unsatisfying) ideas:</p>
  
  <ul>
  <li>share my github credentials with travis via encrypted vars</li>
  <li>create a separate github account for travis</li>
  <li>create separate ssh keys, share with travis (encrypted), add to my github</li>
  </ul>
  
  <p>Does anyone have a better idea?</p>
  
  <hr>
  
  <p>Context: I'm publishing my project from travis.ci and it automatically assigns a new version number that's tracked as a git tag, e.g. <code>v1.0.5</code></p>
  
  <p>Without anything setup, it obviously fails due to missing permissions:
  <code>
  pushing to remote, using `git push origin v0.1.41`
  remote: Invalid username or password.
  fatal: Authentication failed for 'https://github.com/mpollmeier/sbt-ci-release-early-usage.git/'
  </code></p>