Add scss as a supported language for syntax highlighting in documentation

[nshahan]

We commonly document the usage of visual customizations for angular UI components with .scss code. Sometimes it will do an OK job with auto-detection but if you add the scss hint to a triple tick code block it doesn't work well.

scss is a supported language in the highlightjs docs:
https://highlightjs.readthedocs.io/en/latest/css-classes-reference.html#language-names-and-aliases

[isoos]

/cc @jcollins-g: I can update the highlight js resources and create PRs for both repositories.

[isoos]

Updated the related file, will be part of the next release.