MDL-66979 behat: Switch to new W3C Behat driver

This commit updates the composer dependencies to make use of the updated
version of moodlehq/moodle-behat-extension which depends upon the
php-webdriver/webdriver and relevant Mink WebDriver.

composer.json

@@ -4,16 +4,11 @@
     "description": "Moodle - the world's open source learning platform",
     "type": "project",
     "homepage": "https://moodle.org",
-    "repositories": [
-        {
-            "type": "vcs",
-            "url": "https://github.com/moodlehq/php-webdriver.git"
-        }
-    ],
     "require-dev": {
         "phpunit/phpunit": "8.5.*",
-        "moodlehq/behat-extension": "3.400.0",
-        "mikey179/vfsstream": "^1.6",
-        "instaclick/php-webdriver": "dev-local as 1.x-dev"
-    }
+        "moodlehq/behat-extension": "3.400.3",
+        "mikey179/vfsstream": "^1.6"
+    },
+    "minimum-stability": "dev",
+    "prefer-stable": true
 }