[Ruby] match /<regex>/ syntax explictly

[randy3k]

close #923
close #933
close #1006
close #1136

The issue was looking ahead pattern cannot be popped immediately, see sublimehq/sublime_text#1906 (comment)

[wbond]

Excellent, thanks!

[michaelblyons]

This needs a scope test for the / itself. As noted in #1150, it is missing keyword.operator.arithmetic.ruby.

[varyform]

It's better than #1006 (comment)
But the highlighting is still broken:

[gregblass]

I'm experiencing this in my current Sublime Text 3.

When I hit 'Check for updates', it says everything is up to date. I'm guessing this must be part of a package that I have to update?

Is there a recommended process to get this fix?

[gregblass]

So I went to 'Upgrade Packages', but it says none need upgrading.

[gregblass]

I figured it out. Just needed to read the README. Imagine that!