upd CHANGELOG.md

Author: odr

servant-server/CHANGELOG.md

@@ -3,6 +3,10 @@
 
 Package versions follow the [Package Versioning Policy](https://pvp.haskell.org/): in A.B.C, bumps to either A or B represent major versions.
 
+0.20.1
+----
+- Add instance `HasServer (EmptyAPI :> api) context` [#1775](https://github.com/haskell-servant/servant/pull/1775)
+
 0.20
 ----