Let platform be a self-invoked function

lib/utils/platform.js

@@ -2,8 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-utils.platform = {
-  platform: function () {
+utils.platform = (function () {
     let platform = {}
 
     const userAgent = (navigator.userAgent).toLowerCase()
@@ -95,5 +94,4 @@ utils.platform = {
     if (platform.isMozilla) { platform.srcObject = 'mozSrcObject' }
 
     return platform
-  }
-}
+})()