I have updated the license on master and 2.4.x. I think updating 2.3 should be only necessary if we ever release this maintenance branch again. If you guys have some time to check at least master, would be nice (so that we don't discover problems too late, during a release...).
I have also a question regarding how we should update NOTICE [1] and LICENSE [2]. Let me know what you think. [1] https://github.com/groovy/groovy-core/blob/master/NOTICE [2] https://github.com/groovy/groovy-core/blob/master/LICENSE
