Add prismjs alias for `nunjucks` mapped to `jinja2`

[zachleat]

Nunjucks is essentially a port of jinja2

https://mozilla.github.io/nunjucks/templating.html

[zachleat]

Both njk and nunjucks will be aliased to jinja2 on 4.1.0+

[edwardhorsford]

@zachleat this doesn't seem to be working correctly for me, though it does answer why njk and nunjucks aren't erroring for me.

From my reading of this, when I use nunjucks it should look the same as jinja2 however they don't!

With nunjucks:

With jinja2:

It's clearly doing something with the highlighting, but it's not correct, and it's not the same as jinja2. I observe the same when used as a shortcode and when used with markdown backticks. Using plugin v5.0.0