🎨 Implement JS Standard Code Style 7

Updates Standard Code Style to 7 (latest major) and ensures that code
is conform.

 * camelCase is now enforced
 * No assignments in return statements

lib/browser/api/menu-item.js

@@ -89,7 +89,9 @@ MenuItem = (function () {
     if (defaultValue == null) {
       defaultValue = null
     }
-    return this[name] != null ? this[name] : this[name] = defaultValue
+    this[name] != null ? this[name] : this[name] = defaultValue
+
+    return this[name]
   }
 
   MenuItem.prototype.overrideReadOnlyProperty = function (name, defaultValue) {