Bump version to MINOR release 2.8.0

Features:
* Add support for user verification
* Add surface capability shortcut
* Add otherDeviceIds to smart home sync response

Change-Id: I29c59c301b8821f78735012fb88a53cf8cad6d09

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": "2.7.1",
+  "version": "2.8.0",
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {