Remove 'rubinius' from blacklist.rb

Having 'rubinius' in blacklist.rb prevents taps from providing a rubinius formula. Currently, the Rubinius project is making a binary install of Rubinius 2.3.0+ available as a tap. Unfortunately, this is impossible with this blacklist and forces us to use a non-standard name for the formula.

Further, it appears that Homebrew has changed its stance on binary formula, including them in the standard set of formula (ie, not requiring a separate tap). When Homebrew blacklisted Rubinius initially, I asked to allow a binary formula for Rubinius and was refused. The fact that Homebrew has changed its stance on binary formula makes this blacklist doubly unfair.

Thanks.