Add support for erb-lint

[evenreven]

Name: erb-lint
URL: https://github.com/Shopify/erb-lint

erb-lint is a Rubocop-based linter and fixer developed at Shopify for embedded ruby (.html.erb files). It used to be hard to integrate with editors, but this recently changed, and there is now a VS Code integration that works quite well (both as linter and autofixer). I've only used Ruumba (the other Rubocop-based erb linter) for a little while, but from what I can tell the main advantage of erb-lint is that it comes with real HTML parsing and linting as well, i.e. it doesn't just lint the Ruby snippets. (Technically this is done by a different gem called better-html, but it's bundled with erb-lint and you don't have to run it separately.)

I think erb-lint is currently the best linter for this format, and since I use (neo)vim and not VS Code, I'd love to see it supported by ALE! (Sadly I don't know enough to help with a PR.)

[roelandm]

I think it is similar to the Ruumba linter. I'll give it a try.

[evenreven]

Since this is implemented and merged now, I'm closing this issue.