Remove suspicious group inside type parameter character class 

This group was added in 06c314bdb1d876e6dd4d3df64458c4462e6d575e. I'm not sure
what the intent was here. Oniguruma parses (?:+) as regular characters. [,] is
parsed as a nested character class and so is equivalent to just a bare comma.
So the addition of this group to the character class really just means that
parentheses and colons are now part of the (negated) class. I don't believe
this was the intent, so I've removed the group entirely.
Merge pull request #10 from aroben/simpler-type-parsing

Remove suspicious group inside type parameter character class