Fix header casing

[daffl]

See https://github.com/feathersjs/feathers-authentication/blob/master/src/options.js#L5 for the default.

Closes #23

[marshallswain]

[ekryski]

Yeah I think this should be fine. Server side Express lowercases it. The header sent from the client really should be Authorization as that is the HTTP standard. I don't think this will cause any side effects but can't be 100% certain. I'd say

[daffl]

That's what I though. Sounds good. This repo is still 0.x so I'll just make it a 0.2 in case it does break something.