Fixed typo in refetchable-fragments.md (#4427)

Summary: Pull Request resolved: #4427

Reviewed By: alunyov

Differential Revision: D48989050

Pulled By: captbaritone

fbshipit-source-id: 4ba39ba0b1135d7a92d99b896c583e268fdf12c0

Author: yif042

website/docs/tutorial/refetchable-fragments.md

@@ -50,7 +50,7 @@ You should now see a sidebar with a list of people at the top.
 
 ![Contacts list](/img/docs/tutorial/refetchable-contacts-initial.png)
 
-Have a look at `ContactsList.js` and you’ll find this fragment, which is what selects the list of contacts:
+Have a look at `ContactsList.tsx` and you’ll find this fragment, which is what selects the list of contacts:
 
 ```
 const ContactsListFragment = graphql`