Add script boilerplate for ruby

after/ftplugin/ruby_matchup.vim

@@ -1,3 +1,9 @@
+if !exists('b:did_ftplugin')
+  finish
+endif
+
+let s:save_cpo = &cpo
+set cpo&vim
 
 call matchup#util#patch_match_words('retry', 'retry\|return')
 
@@ -5,4 +11,7 @@ let b:match_midmap = [
       \ ['rubyRepeat', 'next'],
       \ ['rubyDefine', 'return'],
       \]
+let b:undo_ftplugin .= '| unlet! b:match_midmap'
+
+let &cpo = s:save_cpo