Correct issue link for exemplar PR (#4174)

Signed-off-by: Evan Torrie <[email protected]>

CHANGELOG.md

@@ -42,7 +42,7 @@ We use _breaking :warning:_ to mark changes that are not backward compatible (re
 - [#4019](https://github.com/thanos-io/thanos/pull/4019) Query: Adds query range histogram.
 - [#3846](https://github.com/thanos-io/thanos/pull/3846) Query: Added federated exemplars API support.
 - [#3350](https://github.com/thanos-io/thanos/pull/3350) Query/Sidecar: Added targets API support. You can now configure you Querier to fetch Prometheus targets from leaf Prometheus-es!
-- [#3977](https://github.com/thanos-io/thanos/pull/3903) Expose exemplars for `http_request_duration_seconds` histogram if tracing is enabled.
+- [#3977](https://github.com/thanos-io/thanos/pull/3977) Expose exemplars for `http_request_duration_seconds` histogram if tracing is enabled.
 - [#3903](https://github.com/thanos-io/thanos/pull/3903) Store: Returning custom grpc code when reaching series/chunk limits.
 - [#3919](https://github.com/thanos-io/thanos/pull/3919) Allow to disable automatically setting CORS headers using `--web.disable-cors` flag in each component that exposes an API.
 - [#3840](https://github.com/thanos-io/thanos/pull/3840) Tools: Added a flag to support rewrite Prometheus TSDB blocks.