Bump version to MINOR release 2.9.0

Features:
* Add support for DigitalPurchaseCheck

Change-Id: I446d84631a6763735b3218dcb392f97f35f10bfd

Author: Canain

package.json

@@ -3,7 +3,7 @@
   "description": "Actions on Google Client Library for Node.js",
   "main": "dist/index.js",
   "types": "dist/index.d.ts",
-  "version": "2.8.0",
+  "version": "2.9.0",
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {