Fix function signature for element properties

Author: justafish

lib/WebDriver/Element.php

@@ -26,7 +26,7 @@
  * @method array location() Determine an element's location on the page.
  * @method array location_in_view() Determine an element's location on the screen once it has been scrolled into view.
  * @method string name() Query for an element's tag name.
- * @method array property($propertyName) Get element property.
+ * @method mixed property($propertyName) Get element property.
  * @method array rect() Get element rect.
  * @method array screenshot() Take element screenshot.
  * @method boolean selected() Is element selected?