Fix fragments docs example JSX typo (#10885)

Fixes https://github.com/facebook/react/issues/10883

docs/reference-react-component.md

@@ -114,9 +114,9 @@ You can also return multiple items from `render()` using an array:
 ```javascript
 render() {
   return [
-    <li key="A"/>First item</li>,
-    <li key="B"/>Second item</li>,
-    <li key="C"/>Third item</li>,
+    <li key="A">First item</li>,
+    <li key="B">Second item</li>,
+    <li key="C">Third item</li>,
   ];
 }
 ```