Update more extension manifests to manifest_version 2

chrome/test/data/extensions/app2/manifest.json

 {
   "name": "Test App 2",
   "version": "1",
+  "manifest_version": 2,
   "permissions": ["unlimited_storage"],
   "app": {
     "urls": [
       "http://www.example.com/path3",
       "http://www.example.com/path4"
     ],
     "launch": {
       "web_url": "http://www.example.com/path4/foo.html"
     }
   }
 }