[DISCUSS] Bump to groovy 2.4.6

[Stephen Mallette <sp...@gmail.com>]

Groovy just released 2.4.6 - I think it's worth bumping to this version for
TinkerPop 3.1.x/3.2.x.  I was scanning through the bug fixes and there are
more than a few items there that I think we should have available to
TinkerPop.  I'm also aware of some code changes that would allow me to drop
some custom code out of TinkerPop that was working around a problem or two
from previous versions of groovy.

Here's the changelog for that version:

http://groovy-lang.org/changelogs/changelog-2.4.6.html

Barring objections in the next three days (Thursday, February 25, 2016 at
6:30am EST), I"ll assume lazy consensus and move forward with the change.