depends_on :cask stanza not working

[jawshooah]

In an attempt to get started on #8492, I added a depends_on :cask => 'cvc4' stanza to the cryptol Cask.

While running brew cask install cryptol, the installer happily ignored the absence of a cvc4 installation:

==> Satisfying dependencies
complete

The dependency seems to be recognized, as shown in the --debug output:

==> Cask instance method 'depends_on':

---
:cask:
- cvc4

So somewhere down the line, the installer either ignores the dependency, or incorrectly concludes that it is satisfied.

[jawshooah]

Scratch that; forgot I didn't install brew-cask with --HEAD. #8491 hasn't made it into a release yet.