update to latest bidict

[jab]

Hi @capcarr, I'm the author of bidict, and saw this project depends on an older version of it. Wanted to give you a heads up that there's a newer version available which fixes bugs in the version you're using, but which also has some breaking API changes (for the sake of a cleaner and safer API) — see https://bidict.readthedocs.org/en/master/changelog.html#id2.

FWIW, I don't expect any further breaking API changes, and hope to release bidict 1.0 soon.

Hope bidict has been working well for you, and please feel free to give feedback here or on Gitter.