title: XBRL R package reads adds another link to input link. Resulting in a link that cannot be opened
body: <p>I'm using XBRL package to import XBRL data from the SEC EDGAR website, and whenever I use xbrlDoAll function, it is unable to read the url, even though I provided the valid one. For example, to replicate this error, use the following:</p>
  
  <pre><code>library(XBRL)
  
  inst &lt;- "https://www.sec.gov/Archives/edgar/data/320193/000032019318000145/aapl-20180929.xml"
  xbrl.vars &lt;- xbrlDoAll(inst)
  </code></pre>
  
  <p>This is the error I get:</p>
  
  <pre><code>Error in fileFromCache(file) : Error in download.file(file, cached.file, quiet = !verbose) : cannot open URL 'https://www.sec.gov/Archives/edgar/data/320193/000032019318000145/https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd'
  </code></pre>
  
  <p>As you can see, the URL cannot be opened because for some reason it adds another https:// in the middle of the link to get the file.</p>
  
  <blockquote>
    <p><a href="https://www.sec.gov/Archives/edgar/data/320193/000032019318000145/https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd" rel="nofollow noreferrer">https://www.sec.gov/Archives/edgar/data/320193/000032019318000145/https://xbrl.sec.gov/dei/2018/dei-2018-01-31.xsd</a></p>
  </blockquote>
  
  <p>Which makes it an invalid url. I tried to manually download the file to the cache folder but the issue still persists. How can I edit it so it can properly read and download the content from the links? Thank you.</p>