docs(gatsby-link): fix link tag typo (#9238)

Fixed a typo in docs where the start `<Link>` tag had a forward slash.

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docs/docs/gatsby-link.md

@@ -68,7 +68,7 @@ render () {
     <Link
       to="/another-page/"
       replace
-    />
+    >
       Go and prevent back to bring you back here
     </Link>
   )