Add CHANGELOG entry

Signed-off-by: Kemal Akkoyun <kakkoyun@gmail.com>

CHANGELOG.md

@@ -32,6 +32,7 @@ We use *breaking* word for marking changes that are not backward compatible (rel
 - [#1666](https://github.com/thanos-io/thanos/pull/1666) `thanos_compact_group_compactions_total` now counts block compactions, so operations that resulted in a compacted block. The old behaviour
 is now exposed by new metric: `thanos_compact_group_compaction_runs_started_total` and `thanos_compact_group_compaction_runs_completed_total` which counts compaction runs overall.
 - [#1748](https://github.com/thanos-io/thanos/pull/1748) Updated all dependencies.
+- [#1694](https://github.com/thanos-io/thanos/pull/1694) `prober_ready` and `prober_healthy` metrics are removed, for sake of `status`. Now `status` exposes same metric with a label, `check`. `check` can have "healty" or "ready" depending on status of the probe.
 
 ## [v0.8.1](https://github.com/thanos-io/thanos/releases/tag/v0.8.1) - 2019.10.14