fix phpstan errors

Author: robocoder

lib/WebDriver/Element.php

@@ -113,7 +113,7 @@ public function getID()
     /**
      * Get the value of an element's attribute: /session/:sessionId/element/:id/attribute/:name
      *
-     * @param string name
+     * @param string $name
      *
      * @return mixed
      */

lib/WebDriver/Session.php

@@ -134,7 +134,7 @@ public function open($url)
      */
     public function capabilities()
     {
-        if (! isset($this->capabilities)) {
+        if ($this->capabilities === null) {
             $result = $this->curl('GET', '');
 
             $this->capabilities = $result['value'];