Fix monkey patch for Rollout 1.2.0

The latest Rollout makes the second argument of `active?` optional -- if
nil it checks if a feature is globally active. Adding the default to the
monkey patch should be backwards compatible with older versions of
Rollout for non-pathological cases since there is no arity change.
Loosen Rollout dependency to accommodate 1.2.0
Merge pull request #15 from ches/rollout-1.2.0

Fix monkey patch for Rollout 1.2.0