Added missing e.stopImmediatePropagation() call in tap handler.
Added missing e.stopImmediatePropagation() call in tap handler.

Otherwise, this leaked event causes issues when this component is loaded inside a `<paper-drawer-panel>`.
https://github.com/PolymerElements/paper-drawer-panel/issues/92

jasongardnerlv/radium-combo,johnyanarella/radium-combo