feat(tooltip): remove unnecessary $digest

- Remove unnecessary call to `$digest`

Closes #4151

Author: wesleycho

Diff for: src/tooltip/tooltip.js

@@ -206,7 +206,6 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position', 'ui.bootstrap
 
               // Set the initial positioning.
               tooltip.css({ top: 0, left: 0, display: 'block' });
-              ttScope.$digest();
 
               positionTooltip();