ipfs uri validation #195

Hello,

Thanks for this awesome library.

I just want to report a tiny issue regarding uri validation:

import validators
uri = "ipfs://someRandomProprietaryAACFile"
validators.url(uri)

The above code returns a ValidationFailure despite the fact that the uri is a valid ipfs uri.
Probably validation does not take into account the ipfs protocol.

Is it possible to add it to validators.url?

Thanks