title: R - install_github fails
body: <p>I am trying to install a package from github in R, however I am getting the following error:</p>
  
  <pre><code>&gt; install_github("jmp75/rClr", build_vignettes=TRUE)
  Downloading github repo jmp75/rClr@master
  Error in curl::curl_fetch_memory(url, handle = handle) : 
  Peer certificate cannot be authenticated with given CA certificates
  </code></pre>
  
  <p>I have set the RCurl options as such:</p>
  
  <pre><code>options(RCurlOptions = c(getOption("RCurlOptions"),   ssl.verifypeer = FALSE,  ssl.verifyhost = FALSE ) )
  </code></pre>
  
  <p>After checking the setting:</p>
  
  <pre><code>getOption("RCurlOptions")
  </code></pre>
  
  <p>we see....</p>
  
  <pre><code>$cainfo
  [1] "C:/_CODE/R/Library/RCurl/etc/ca-bundle.crt"
  
  $ssl.verifypeer
  [1] FALSE
  
  $ssl.verifyhost
  [1] FALSE
  </code></pre>
  
  <p>Still I get the error:</p>
  
  <pre><code>Downloading github repo jmp75/rClr@master
  Error in curl::curl_fetch_memory(url, handle = handle) : 
  Peer certificate cannot be authenticated with given CA certificates
  </code></pre>
  
  <p>any clues</p>