regexp: prevent ")" inside character class from terminating group

/([)])/ is currently not handled correctly: the first ")" mistakenly
terminates the jsRegexpGroup and consequently the jsRegexpCharClass,
since the former contains the latter.

This commit adds a skip pattern to prevent a ")" character inside a
character class from terminating a jsRegexpGroup.
Merge pull request #214 from davidchambers/regexp

regexp: prevent ")" inside character class from terminating group