adapted build to Groovy compiler related change in latest Gradle
adapted build to Groovy compiler related change in latest Gradle

GeeChao/spock,raphw/spock,psideleau/spock,sebi-hgdata/spock,alien11689/spock,alien11689/spock,sebi-hgdata/spock,paplorinc/spock,leonard84/spock,GeeChao/spock,raphw/spock,lokinell/spock,siordache/spock,siordache/spock,psideleau/spock,lokinell/spock,siordache/spock,psideleau/spock,paplorinc/spock,paplorinc/spock,sebi-hgdata/spock,alien11689/spock,lokinell/spock,spockframework/spock,raphw/spock,GeeChao/spock