Enable the object-shorthand ESLint rule

Please see http://eslint.org/docs/rules/object-shorthand.

Unfortunately, based on commit 9276d1dcd9, it seems that we still need to maintain compatibility with old Node.js versions, hence certain files/directories that are executed in Node.js are currently exempt from this rule.

Furthermore, since the files specific to the Chromium extension are not run through Babel, the `/extensions/chromium/` directory is also exempt from this rule.

gulpfile.js

@@ -13,6 +13,7 @@
  * limitations under the License.
  */
 /* eslint-env node */
+/* eslint-disable object-shorthand */
 /* globals target */
 
 'use strict';