chore(deps): update dependency wp-cli/wp-cli to v2 (GoogleCloudPlatform#1326)

Author: renovate-bot

appengine/flexible/wordpress/files/composer.json

@@ -3,6 +3,6 @@
         "google/cloud": "~0.21"
     },
     "require-dev": {
-        "wp-cli/wp-cli": "~1.1"
+        "wp-cli/wp-cli": "~2.0"
     }
 }