Feature prune: fix sed command

The asterisk moved causing the sed to not remove anything
Feature prune: return early if there are no branches to prune
Fix .gitignore to truly ignore plugins folder
Feature Prune: don't output branches in branch test

If there are branches that need to be pruned, they should only be
outputted once
Feature prune: minor tweaks

Use ruby %{} to avoid escaping double quotes, add sed to remove leading
whitespace
Feature prune: simplify call to shell
Merge pull request #119 from iFixit/feature-prune--fix-current-branch-case

Feature prune: fix sed pipe