Remove unsupported chromedriver-helper, make use of webdrivers in hyper-spec

[adamcreekroad]

chromedriver-helper has been unsupported for a while now in favor of webdrivers. webdrivers is included in the hyper-spec gemfile, but isn't actually used.

I usually end up fighting against chromedriver-helper, and lately it's installing a beta version that doesn't support the latest normal release of chrome. This prevents any of the specs from running for me. Removing chromedriver-helper and making use of webdrivers is working perfectly, and it also simplifies the travis-ci config a bit.

Unless there's a specific reason we're using chromedriver-helper, I think this will help clean the development environment a bit.