fix(typo): the tag closed itself (#1089)

Author: ThaddeusJiang

docs/example-react-router.mdx

@@ -169,8 +169,8 @@ In React Router v5, you need to pass the history object as a whole to the Route
 test('full app rendering/navigating', () => {
   const history = createMemoryHistory()
   render(
-    <Router history={history} />
+    <Router history={history}>
       <App />
     </Router>,
   )
-  ```
+  ```