`spec` is the same variable name as gemspec generated by bundler, and its
intention is easier to understand than a one-letter variable.
https://github.com/bundler/bundler/blob/00fd58eaa69015092ee272c4cb5aa92a5e7ee45c/lib/bundler/templates/newgem/newgem.gemspec.tt#L11

This is follow up 685cf0d5. `spec` is already in use there.