Unable to get syntax highlighting to work

[paniash]

I followed the method mentioned in the pull request for syntax highlighting using hightlight.js, however I'm unable to get it to work.

layouts/partials/foot_custom.html:

<script src="//yihui.name/js/math-code.js"></script>
<script async src="//mathjax.rstudio.com/latest/MathJax.js?config=TeX-MML-AM_CHTML"></script>

<script async src="//yihui.name/js/center-img.js"></script>

<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.3/highlight.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.3/languages/r.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.3/languages/python.min.js"></script>

<script>
hljs.configure({languages: []});
hljs.initHighlightingOnLoad();
</script>

layouts/partials/head_custom.html:

<link href="https;//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.18.3/styles/gruvbox-dark.min.css" rel="stylesheet">

static/css/fonts.css:

/* code */
pre {
  border: 1px solid #3A3E41;
  /* box-shadow: 5px 5px 5px #000; */
  background: #f8f8f8;
  padding: 1em;
  overflow-x: auto;
}
code { background: #181A1B; }
pre code { background: none; }