Symbol literal (%i or %I) highlighting

Ruby has added the cool new literal `%i` (and its interpolated counterpart `%I`) to build an array of symbols, just as `%w` builds an array of strings.

I've managed to modify the Language definition to highlight those literals as others literals.

It would definitely be better not to color them as strings, but as symbols, but the Language definition in Textmate is way too complicated for me.