After upgrading ES to 2.1.0, ES won't start anymore and following lines appear in the log:
[2015-11-27 17:18:27,660][ERROR][bootstrap ] Exception
java.lang.IllegalArgumentException: Plugin [license] is incompatible with Elasticsearch [2.1.0]. Was designed for version [2.0.0]
It seems I have to update the license, but how do I do that?