isCapable = function isCapable() {
	  var hasNotificationSupport = ('Notification' in window);
	  var hasPromiseSupport = typeof Promise === 'function';
	  return isBrowser() && hasNotificationSupport && hasPromiseSupport;
	}
Checks if browser notification support exists.

@public
@see {@link https://caniuse.com/#feat=notifications|Browser support (notifications)}
@see {@link https://caniuse.com/#feat=promises|Browser support (promises)}
@see {@link Mocha#growl}
@see {@link Mocha#isGrowlCapable}
@return {boolean} whether browser notification support exists