Revert "Prevent ctags from spawning multiple times"

This reverts commit dad8d44973f252b93afd4a61a9677aad4180d956.
Exclude node_modules from ctags

This was creating ~76MB tag files in the popit repository, which was
reduced to 1.5MB with this change. This should also speed up backups as
the tag file changes won't be as big.
Change license script to have a header

And refactor it a bit
Default to ruby 2.1

For super speedy rubies :speedboat: