Add include/extend/prepend to Ruby keywords

[janko]

In Ruby, include, extend and prepend are treated as keywords (e.g. GitHub's syntax highlighter has that behaviour), so I thought it would be nice if Prism did this as well.

By the way, I'm generally impressed with Prism's Ruby tokenization, especially coming from highlight.js.

[RunDevelopment]

Thank you for submitting this PR!

Please run gulp to generate the minified files and please add the new keywords to Ruby's keyword test.

[RunDevelopment]

Ooof. Seems like npm installed a more recent version of UglifyJS for you.
Could you please tell me which version because npm only installs v3.5.2 for me. You can check by opening path/to/prims/node_modules/uglify-js/package.json. At the end of the file, there will a version property.

[mAAdhaTTah]

@RunDevelopment npm ls uglify-js would be easier.

@janko Use npm ci to make sure you get the exact versions in the lockfile.

[janko]

Thanks for the instructions. I've actually switched to Atom's highlights package, which uses the "official" Ruby grammar (it's used by GitHub, Atom and VSCode). This grammar is more robust and highlights all Ruby code correctly for me, and is up-to-date with these new keywords.