add mention of upgrade to Unicode 10.0.0 to NEWS file

(this completes [Feature #13685]; [ci skip])

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59761 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

NEWS

@@ -81,7 +81,7 @@ with all sufficient information, see the ChangeLog file or Redmine
     [Feature #7688]
 
 * Regexp
-  * Update Onigmo 6.1.1.
+  * Update to Onigmo 6.1.1.
     * Support absent operator https://github.com/k-takata/Onigmo/issues/82
 
 * String
@@ -99,6 +99,8 @@ with all sufficient information, see the ChangeLog file or Redmine
   * String#each_grapheme_cluster and String#grapheme_clusters is added to
     enumerate grapheme clusters [Feature #13780]
 
+* Regexp/String: Updated Unicode version from 9.0.0 to 10.0.0 [Feature #13685]
+
 * Thread
 
   * Thread#fetch  [Feature #13009]