title: unable to access index for repository in R
body: <p>I am on Windows 7 and I am using R Studio 0.99.902 with R3.3.1. When I am trying to install a package I get the Warnings:</p>
  
  <pre><code>Warning: unable to access index for repository http://cran.rstudio.com/src/contrib:
    cannot open URL 'http://cran.rstudio.com/src/contrib/PACKAGES'
  Warning: unable to access index for repository http://www.stats.ox.ac.uk/pub/RWin/src/contrib:
    cannot open URL 'http://www.stats.ox.ac.uk/pub/RWin/src/contrib/PACKAGES'
  </code></pre>
  
  <p>It is the first time I see it and I cannot solve it. Can anyone help me ?</p>