Make ERB tags easier to find

[roelandmoors]

It would be nice if ERB tags could get some extra color or style.
Now it is a bit hard to see where the ERB tags are.

[roelandmoors]

I added this for now:
call s:hi("erubyDelimiter", s:nord15_gui, "", s:nord15_term, "", "", "")

[arcticicestudio]

Hi @roelandmoors 👋, thanks for your contribution 👍

Actually it should be colored with nord10 due to the default linking to the PreProc groups so I wonder why its not working. Anyway, feel free to submit a PR which explicitly adds this syntax group.