add leniency to the command line

Created by: kbrock

Hi,

Very cool that the commands to rerun specs is at the bottom of a test run. And I often copy and paste the sample commands to rerun them.

Unfortunatly, I often type bundle exec rspec first, so I end up with 2 rspec commands on the line:

bundle exec rspec rspec ./spec/file_spec.rb

This PR ignores a duplicate rspec command.

It is (my) user error, but it happens enough that I would imagine that others do the same.

Thanks