* ext/date/date_core.c: [DOC] plural grammar fixed by @scott113341
  Contributed via documenting-ruby.org: documenting-ruby/ruby#16
  https://github.com/documenting-ruby/ruby/pull/16


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43315 b2dd03c8-39d4-4d8f-98ff-823fe69b080e