Using fzf to select specs to run

Use FZF to select multiple spec files that are either changed or staged, run rspec and add the command created to zsh history so that we can rerun the command with <up-arrow>:

rsf() {
  FILES=$(git status -vv -s spec/* | fzf --multi | awk '{print $2}')

  print -s bin/rspec $FILES
  bin/rspec $FILES
}