Track should allow hash arguments to be strings

[shipstar]

I'm enqueuing a tracking job in Redis that consists of a simple hash. When the hash is deserialized, it's no longer a Hash#with_indifferent_access, so the keys come in as strings.

I'm manually calling Hash#with_indifferent_access, but it seems fairly rigid to require the keys to be symbols.

I can submit a pull request if it makes sense.

[calvinfo]

I'm not opposed to this idea, I'd like to see how the code for it looks. Definitely submit a pull request. As long as it is clean, backwards compatible, and doesn't add new dependencies, I'm cool with it. :)

[calvinfo]

Fixed by #16