Make ruby-guard play nicely with fuubar

 * https://github.com/thekompanee/fuubar is an rspec
   progress bar formatter that uses
   https://github.com/jfelchner/ruby-progressbar to format
   the line without a bunch of dots - just fills the screen
   The emacs *guard* buffer didn't support the fancy
   cursor positioning and adding `|cat` to the command
   makes ruby-progressbar fallback to "nontty" mode.