phantomjs not available anymore on homebrew

[ciscoheat]

The never ending story.

> brew update
Updated 1 tap (homebrew/core).
==> Updated Formulae
citus
> brew install phantomjs
Error: No available formula with the name "phantomjs" 
It was migrated from homebrew/core to homebrew/cask.
You can access it again by running:
  brew tap homebrew/cask
And then you can install it by running:
  brew cask install phantomjs

https://travis-ci.org/ciscoheat/dataclass/jobs/449335985#L1474-L1485

[kevinresol]

I think we should migrate to chrome #80