Mention the addition of Enumerator::Yielder#to_proc in NEWS

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67213 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -30,6 +30,14 @@ Enumerable::
 
    * Added Enumerable#tally.  [Feature #11076]
 
+Enumerator::
+
+  New method::
+
+   * Added Enumerator::Yielder#to_proc so that a Yielder object can be
+     directly passed to another method as a block argument.
+     [Feature #15618]
+
 Regexp/String::
 
     * Update Unicode version and Emoji version from 11.0.0 to 12.0.0.