fix(tooltip): fix positioning error when appendToBody is set to true

Closes angular-ui#387

use offset function instead position function when appednToBody is set to true

src/tooltip/tooltip.js

@@ -167,9 +167,9 @@ angular.module( 'ui.bootstrap.tooltip', [ 'ui.bootstrap.position' ] )
             } else {
               element.after( tooltip );
             }
-            
+
             // Get the position of the directive element.
-            position = $position.position( element );
+            position = options.appendToBody ? $position.offset( element ) : $position.position( element );
 
             // Get the height and width of the tooltip so we can center it.
             ttWidth = tooltip.prop( 'offsetWidth' );