Add welcome-page and rootURL to BUILT_INS in template-no-implicit-this

Author: johanrd

lib/rules/template-no-implicit-this.js

@@ -26,6 +26,9 @@ const BUILT_INS = new Set([
   'textarea',
   'query-params',
   'unique-id',
+  // arg-less components/helpers from the default ember-cli blueprint
+  'welcome-page',
+  'rootURL',
 ]);
 
 // Control-flow built-ins whose params should not be flagged