title: remove facebook and twitter links in `bookdown` in R, Rmarkdown
body: <p>I am using the <code>bookdown</code> package in R to write a gitbook, but I don't want the final book to have the sharing links to facebook, twitter. I am using something like this in the <code>YAML</code></p>
  
  <pre><code>--- 
  title: "A Minimal Book Example"
  author: "SN"
  date: "`r Sys.Date()`"
  output: 
    bookdown::gitbook
      gitbook_config:
        sharing:
          facebook: false
          twitter: false
  documentclass: book
  link-citations: yes
  description: "This book ... ."
  ---
  </code></pre>
  
  <p>but I am getting an error</p>
  
  <pre><code>Error in yaml::yaml.load(enc2utf8(string), ...) : 
    Scanner error: mapping values are not allowed in this context at line 6, column 19
  Calls: &lt;Anonymous&gt; ... yaml_load_utf8 -&gt; mark_utf8 -&gt; &lt;Anonymous&gt; -&gt; .Call
  Execution halted
  </code></pre>
  
  <p>Can anyone help me in setting options in <code>YAML</code> so that no sharing options show up in the final rendering?</p>
  
  <p>thanks!
  SN</p>