update Groovy to 2.3.7

Change-Id: I6a5cb9d3a5f760d852015934120297b62073c1a3
Reviewed-on: http://gerrit.esdi-community.eu/3566
Tested-by: Jenkins <sitemple@igd.fraunhofer.de>
Reviewed-by: Simon Templer <simon@wetransform.to>