Upgrade Aether and remove dependency on aether-connector-wagon

It is currently not possible to use Shrinkwrap as part of a project that depends on a version of Aether more recent than 0.9.M2. This is because Shrinkwrap depends on the artifact aether-connector-wagon which seems to have been replaced in newer versions of Aether by aether-connector-basic and aether-transport-wagon.

Upgrading this dependency would allow users depending on newer versions of Aether to use Shrinkwrap.