Docs: Upgrade highlight.js to 9.0.0

Docs: Upgrade highlight.js to 9.0.0

with the following added languages in anticipation of document expansion:

    apache dockerfile dos less php powershell python tex yaml

To reproduce docs/static/js/highlight.pack.js on Debian/Ubuntu:

    $ sudo apt-get install nodejs npm
    $ wget https://github.com/isagalaev/highlight.js/archive/9.0.0.tar.gz
    $ tar xzf 9.0.0.tar.gz
    $ cd highlight.js-9.0.0/
    $ npm install
    $ nodejs tools/build.js markdown asciidoc xml css javascript \
      ini yaml json go bash diff dockerfile dos powershell makefile \
      apache nginx tex http php python ruby django haml handlebars \
      scss less coffeescript

Then, copy the resulting build/highlight.pack.js as well as
src/styles/monokai-sublime.css to the appropriate Hugo docs directories.