title: Problem with Google Analytics Code in RMarkdown head tag using YAML options "includes:" and "in_head"
body: <p>I have a github page produced from a rmarkdown script. I want to insert the google tracking code into the header and have <a href="https://stackoverflow.com/questions/41376989/how-to-include-google-analytics-in-an-rmarkdown-generated-github-page">followed the advice here</a> without success. I copy my google tacking code into a text file and save it as a .html file. When I include the code: </p>
  
  <p></p>
  
  <pre><code>title: "R Notebook"
  output:
    html_document:
      include:
        in_header: woo.html
  ---
  </code></pre>
  
  <p>The google tracking code comes out in the rendered HTML file at the top of the page. When I look at raw the html file, the tracker code is indeed in the opening   but there is a lot of HTML added to the google analytics tracker. How do I convince RMarkdown to just include the tracker code in the head without printing anything on my html file?</p>