Define String#underscore if it's not already defined
Define String#underscore if it's not already defined

The ActiveSupport condition is overkill, since AS would have already
defined String#underscore

lunalium/sucker_punch,kntmrkm/sucker_punch,danimashu/sucker_punch,grosser/sucker_punch,bethesque/sucker_punch,brandonhilkert/sucker_punch