title: blogdown won't render LaTeX when I'm offline
body: <p><em>I'm using blogdown on an Ubuntu 18.04 system, my 'LaTeX' is TinyTeX, and R is v3.5.2. All my packages are up to date, just ran a <code>update.packages(ask = FALSE, checkBuilt = TRUE)</code> and <code>tinytex::tlmgr_update()</code>.</em></p>
  
  <hr>
  
  <p>And now the issue: LaTeX equations, and everything else, renders fine when I issue the <code>blogdown::serve_site()</code> command from R Studio. When I'm offline (say on a plane) LaTeX equations won't render at all in blogdown. Instead of the rendered equation I get the code, eg:</p>
  
  <pre><code>$$\sigma = \sqrt{ \sum_{i=1}^N \frac{(x_i - \overline{x})^2}{N}}$$
  </code></pre>
  
  <p>Why is this? What should I do? It's not that big of a deal because I can actually see the rendered equations in R Studio. Just not on my served site. </p>
  
  <p>Another interesting thing is that code snippets wrapped in triple tick marks ``` aren't properly rendered either.</p>
  
  <p>What I get is this (notice zebra stripe background):</p>
  
  <p><a href="https://i.stack.imgur.com/Erdnnb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Erdnnb.png" alt="zebra stripes"></a></p>
  
  <p>When I expect to get this (solid grey background):</p>
  
  <pre><code>   2           123
     3           132
     4           131
     5           127
     6           117
     7           120
     8           124
  </code></pre>
  
  <p>When I'm back online with WiFi, and I re-render with <code>blogdown::serve_site()</code> it all looks fine again. Everything renders properly.</p>
  
  <hr>
  
  <p><strong>EDIT:</strong> Minimum reproducible would be a default blogdown site with the LaTeX equation shown above. Should I zip that up and post somewhere to help? </p>
  
  <p>I added this to my YAML but it didn't seem to help:</p>
  
  <pre><code>output:
    html_document:
      mathjax: local
      self_contained: false
  </code></pre>
  
  <p>My browser console output is below.</p>
  
  <pre><code>cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/github.min.css:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
  (index):1 [Intervention] Slow network is detected. See https://www.chromestatus.com/feature/5636954674692096 for more details. Fallback font will be used while loading: http://127.0.0.1:4321/fonts/lato-v11-latin-regular.woff2
  (index):1 [Intervention] Slow network is detected. See https://www.chromestatus.com/feature/5636954674692096 for more details. Fallback font will be used while loading: http://127.0.0.1:4321/fonts/merriweather-v13-latin-regular.woff2
  cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/highlight.min.js:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
  cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/languages/r.min.js:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
  cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/languages/yaml.min.js:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
  (index):194 Uncaught ReferenceError: hljs is not defined
      at (index):194
  cdnjs.cloudflare.com/ajax/libs/mathjax/2.7.5/MathJax.js?config=TeX-MML-AM_CHTML:1 Failed to load resource: net::ERR_INTERNET_DISCONNECTED
  </code></pre>