fix(tooltip): incorrect position when text wraps

The $digest that was removed in 32c470 is actually necessary to get the
tooltip contents rendered. The rendered content is important when the
tooltip is on the right edge. See Plunker in #2995:
http://plnkr.co/edit/8GZ5F5zj3Xe6IinXQz74?p=preview

Fixes #2995

Correctly fixes #2951 without removing $digest.