Bump version to MINOR release 2.12.0

Features:
* Add support for order reservations

Change-Id: I41ad0976b5c1bb06b0701b15f42fd8b6c20164b2

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": "2.11.0",
+  "version": "2.12.0",
   "license": "Apache-2.0",
   "author": "Google Inc.",
   "engines": {