fixup! 355: Support deleting/changing custom surrounds

Author: halostatue

import/surround.vim

@@ -54,7 +54,7 @@ enddef
 def CustomSurroundings(char: string, d: dict<any>, trim: bool): list<string>
   var all = Process(get(d, printf('surround_%d', char2nr(char))))
   var before = ExtractBefore(all)
-  var after = ExtractBefore(all)
+  var after = ExtractAfter(all)
 
   return trim ? [trim(before), trim(after)] : [before, after]
 enddef