title: Disable Travis-CI for pull requests
body: <p>I have a project that uses Travis-CI to build and <code>rsync</code> a static website. I use the following to ensure that this only occurs in <code>master</code>.</p>
  
  <pre><code>branches:
    only:
      - master
  </code></pre>
  
  <p>However, when someone makes a pull request on the repository, Travis-CI prospectively merges that branch into master and does the build and <code>rsync</code>, meaning that anyone could replace the contents of my website with anything by submitting a pull request.</p>
  
  <p><strong>Is there a way to prevent Travis-CI from attempting to build pull requests?</strong></p>