cabal-install: update to version 1.18.0.1

Some quick notes:

* ```cabal-install-1.18.0.1``` includes sandboxing support; facilitating resolution of #21335
* formula no longer puts stuff in ```~/.cabal```, ```~/.ghc``` or elsewhere under ```$HOME``` at install time

That's about it.

Apologies this stuff is taking so long… after I dropped the ```cabal-dev``` stuff for the native sandboxes, I've been kind of swamped (studies, moving, etc.). Close now though. Going to try and get things wrapped up tonight or tomorrow.