Upgrade gem dependencies
Remove hard coded class from let statement
Add spec for IceNine::CoreExt::Object to cover mutation
Add rbx-19mode back into testing matrix temporarily

* Update travis configuration to match other gems
Fix rubocop warning
Update travis to test building without bundler

* ruby-head seems to trip up on this step for some reason. I want to
  test and see if this is the only current blocker to testing with
  ruby-head or not.
Add rbx-19mode to list of rubies allowed to fail with travis
Merge branch 'master' of https://github.com/dkubb/ice_nine into speed-up-recursion-guard
Don't delete object IDs from recursion guard

This prevents some possible revisiting of object (IDs) and kills a
TooManyStatements warning