Bump minimum ruby-progressbar version to 1.4 so we can get the '#started?' method
Remove the intermediate 'progress' let call so we always get the most up-to-date one
Create the bar after 'start' is called so that we can make sure that we get any of the custom options that could be passed in with the RSpec configuration value - Closes #65
Version Bump to 2.0.0.beta2