title: Install R packages from github downloading master.zip
body: <p>I probably have some issues in my connectivity (some sort of blocks, I don't know) and I can't install directly form <code>gitHub</code></p>
  <pre><code>&gt; install_github(&quot;assertthat&quot;)
  Installing github repo(s) assertthat/master from hadley
  Installing assertthat.zip from https://github.com/hadley/assertthat/archive/master.zip
  </code></pre>
  <p>I tried with lots of other packages, same result. However, I am able to download <code>master.zip</code> form the browser. Can you tell if it's possible install directly the <code>.zip</code>? thanks.</p>