Update to Babel 6.
Update to Babel 6.

As part of the work for ember-cli@2.13, all "built in" addons are being updated to use ember-cli-babel@6.

ember-cli-babel@6 requires node 4+, so this also bumps the minimum engine version.

This should be published as 3.0.0.
locks/ember-welcome-page,locks/ember-welcome-page