NXCM-5406: Bump Nx version

Where fixed nexus-client-core resides.
NXCM-5406: Fixed DownloadMojo

No need to fiddle directly with Aether/Status
when Client factory can be instructed using
Conditions to allow to connect only against
certain versions and editions of Nexus
Merge pull request #45 from sonatype/nxcm-5406-work-with-mvn31

NXCM-5406: Make plugins work with Maven 3.1