Revert "upgrade to Groovy 1.8.9"

This reverts commit e4013a7bcc3718f46d8707d13fd44e8e2264e921.
Merge branch '2.1.x' into 2.2.x

Conflicts:
	build.gradle
	grails-bootstrap/src/main/groovy/org/codehaus/groovy/grails/resolve/GrailsCoreDependencies.java