Let --update also check :override-deps

[plexus]

We were checking :deps and :extra-deps but not :override-deps. Since the regular
check also considers this key, --update should to.

Note that you can still opt out of updating certain versions with
^:depot/ignore, either on the version map or on the deps map.

Closes #9

[Olical]

Well, that was quick, looks great too. I like the refactor into update-key. The zipper rewriting is really neat, I need to explore it some more. Great choice of tools!

I think I'll write a test suite on a rainy day that tests all of these data manipulating functions in isolation so we can lock some of this functionality down. I'm sorry I didn't have a test suite in the first place, I spent most of my time stressing about how to look things up in maven while trying to get this working 😬

[plexus]

There's always room for improvement :) thanks for a great tool! It's the kind of thing I would have written myself if you hadn't already, so happy to lend a hand.