Fix bad link

Author: thomaseizinger

core/CHANGELOG.md

@@ -34,7 +34,7 @@
   and `upgrade::read_one` (see [PR 2213]).
 
 - Add `SignedEnvelope` and `PeerRecord` according to [RFC0002] and [RFC0003]
-  (see [PR 2107).
+  (see [PR 2107]).
 
 [PR 2145]: https://github.com/libp2p/rust-libp2p/pull/2145
 [PR 2213]: https://github.com/libp2p/rust-libp2p/pull/2213