Update app.ts (#27673)

fix typo

public/app/app.ts

@@ -113,7 +113,7 @@ export class GrafanaApp {
         $httpProvider: angular.IHttpProvider,
         $provide: angular.auto.IProvideService
       ) => {
-        // pre assing bindings before constructor calls
+        // pre assign bindings before constructor calls
         $compileProvider.preAssignBindingsEnabled(true);
 
         if (config.buildInfo.env !== 'development') {