title: Error when trying to knit html in R markdown
body: <p>Below is the error I am getting:</p>
  
  <blockquote>
  <pre><code>Quitting from lines 46-48 (lesson3_student.rmd) 
  Error in contrib.url(repos, "source") : 
    trying to use CRAN without setting a mirror
  Calls: &lt;Anonymous&gt; ... withVisible -&gt; eval -&gt; eval -&gt; install.packages -&gt; contrib.url
  In addition: Warning message:
  In in_dir(opts_knit$get("root.dir") %n% input_dir(), evaluate::evaluate(code,  :
    You changed the working directory to /Users/Madiyar/Desktop/Facebook Data (probably via setwd()). It will be restored to /Users/Madiyar/Downloads. See the Note section in ?knitr::knit
  Execution halted
  </code></pre>
  </blockquote>
  
  <p>Thanks for help</p>