exclude groovy-all as a transitive dependency from gpars

Pulling in another version of Groovy is causing problems...

Caused by: groovy.lang.GroovyRuntimeException: Conflicting module versions. Module [groovy-all is loaded in version 2.3.1-SNAPSHOT and you are trying to load version 2.1.9
Merge branch 'master' of github.com:grails/grails-core