def validate_no_existing_tag(tag_string)
      existing_tags = []
      @gitrepo.tags.each { |tag| existing_tags << tag.name }
      if existing_tags.include?(tag_string)
        ui.error 'This version tag has already been committed to the repo.'
        ui.error "Are you sure you haven't released this already?"
        exit 6
      end
    end
def validate_no_existing_tag(tag_string)
      existing_tags = []
      @gitrepo.tags.each { |tag| existing_tags << tag.name }
      if existing_tags.include?(tag_string)
        ui.error 'This version tag has already been committed to the repo.'
        ui.error "Are you sure you haven't released this already?"
        exit 6
      end
    end
Ensure that there isn't already a git tag for this version.