NEWS: required keyword arguments

* NEWS (Language changes): mention about required keyword arguments.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43037 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2013-09-25

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43038 b2dd03c8-39d4-4d8f-98ff-823fe69b080e