core: Update the version of the deploy plugin

The version used by default doesn't support the
"altReleaseDeploymentRepository" and "altSnapshotDeployment"
configuration parameters that are convenient in order to deploy to
alternative respositories without changing the POMs.

This patch updats the version to 2.8.1.

Change-Id: Ib19fd5d443531623ecf17329f8e6a0cce9f9b920
Related: https://bugzilla.redhat.com/1069196
Signed-off-by: Juan Hernandez <juan.hernandez@redhat.com>