Fix my-files example code (#2386)

Example code gives React warning about unique "key" prop.
gatsbyjs · Oct 10, 2017 · 7e5171d · 7e5171d
1 parent 2bc8bf4
commit 7e5171d
Showing 1 changed file with 2 additions and 2 deletions.
diff --git a/docs/tutorial/part-four/index.md b/docs/tutorial/part-four/index.md
@@ -401,8 +401,8 @@ export default ({ data }) => {
           </tr>
         </thead>
         <tbody>
-          {data.allFile.edges.map(({ node }) =>
-            <tr>
+          {data.allFile.edges.map(({ node }, index) =>
+            <tr key={index}>
               <td>
                 {node.relativePath}
               </td>