Add ability to bypass dependency check.

[ryanpcmcquen]

Now possible: https://github.com/ryanpcmcquen/image-ultimator/commit/5b5ceb94a8aa830fe0e5273772fb86bce1cb15db

@milojennings you may find this useful.

[milojennings]

Excellent

[milojennings]

How do you use it? Has the documentation been updated?

[ryanpcmcquen]

Per the source:

## override with DEPENDENCY_CHECKER=off
DEPENDENCY_CHECKER=${DEPENDENCY_CHECKER:-on}

I'd rather not put this directly in the documentation, because I want the people who use it to see what is really happening when they override it.

[ryanpcmcquen]

So you would run:

DEPENDENCY_CHECKER=off imgult