tweaks for PR#251
GROOVY-6365: avoid additional wrapping of Object[] into Object[]
Bintray JCenter added as a first resolver in the default Ivy chain.
The resolution should be much faster now: this repo is much faster than the former first resolver (codehaus) and it contains most of the content from most of the popular Java repositories, which means most of the artifacts will be resolved without trying other repositories in the chain.