Update using-with-vuex.md to include namespaced:true in using modules section (#1636)

* Update using-with-vuex.md

* chore: lint

Co-authored-by: Lachlan <[email protected]>

Author: An-AngryBear

docs/guides/using-with-vuex.md

@@ -233,7 +233,8 @@ describe('MyComponent.vue', () => {
         myModule: {
           state,
           actions,
-          getters: myModule.getters
+          getters: myModule.getters,
+          namespaced: true
         }
       }
     })