added bypass_sign_in for next version of Devise

[KendallPark]

I'm working off the Devise master branch and getting these annoying deprecation warnings.

The next version of Devise will deprecate the use of :bypass in the sign_in method. heartcombo/devise#4078 .

This is a little preemptive, but I've updated devise_token_auth for when the next version of Devise is released. All tests still pass. I didn't know how to test it against Devise's master branch but at the very least you can see there's no more deprecation warnings on my tests:

[booleanbetrayal]

thanks for this @KendallPark !