docs: add missing comma (#11976)

Add missing comma

Author: tonytkachenko

docs/configuration/overview.mdx

@@ -239,7 +239,7 @@ export default buildConfig({
   // ...
   // highlight-start
   cors: {
-    origins: ['http://localhost:3000']
+    origins: ['http://localhost:3000'],
     headers: ['x-custom-header']
   }
   // highlight-end