Update Gemfile.lock to use HTTPS for Rubygems
Change output variables in specs to be `let`'s instead
Change progressbar variables in specs to be `let`'s instead
Do not output multiple bars if `#finish` is called multiple times
Do not output the bar multiple times if `#stop` is called when the bar is already stopped
Do not output the bar multiple times if `#resume` is called when the bar is already started
Default to a non-TTY-safe format if there is no TTY support when outputting the bar
Whitespace
Merge branch 'feature/add-better-non-tty-support' into development - Thanks @gurgeous!! - Closes #57

* feature/add-better-non-tty-support:
  Whitespace
  Default to a non-TTY-safe format if there is no TTY support when outputting the bar