Re-added gulp-ng-annotate

Seems like the added dependency in `12b8cbc` got removed incorrectly due to a merge conflict with `e59a36f`.

package.json

@@ -25,6 +25,7 @@
     "gulp-minify-css": "^0.3.4",
     "gulp-minify-html": "^0.1.6",
     "gulp-ng-html2js": "^0.1.8",
+    "gulp-ng-annotate": "^0.3.5",
     "gulp-rename": "^1.2.0",
     "gulp-replace": "^0.3.0",
     "gulp-sass": "ajoslin/gulp-sass#master",