Replace `scope` with `bindings`.

Components should use `bindings` rather than `scope` to declare inputs
and outputs.

src/sidebar/directive/loggedout-message.js

@@ -6,7 +6,7 @@ module.exports = {
   controller: function (serviceUrl) {
     this.serviceUrl = serviceUrl;
   },
-  scope: {
+  bindings: {
     /**
      * Called when the user clicks on the "Log in" text.
      */