Prepare v2.1.1

Signed-off-by: Sora Morimoto <sora@morimoto.io>

Author: smorimoto

CHANGELOG.md

@@ -8,6 +8,8 @@ and this project adheres to
 
 ## [unreleased]
 
+## [2.1.1]
+
 ### Changed
 
 - Do not install `opam-depext` if using opam 2.2 or later.
@@ -476,7 +478,8 @@ that require it.
 
 - Initial release.
 
-[unreleased]: https://github.com/ocaml/setup-ocaml/compare/v2.1.0...HEAD
+[unreleased]: https://github.com/ocaml/setup-ocaml/compare/v2.1.1...HEAD
+[2.1.1]: https://github.com/ocaml/setup-ocaml/compare/v2.1.0...v2.1.1
 [2.1.0]: https://github.com/ocaml/setup-ocaml/compare/v2.0.21...v2.1.0
 [2.0.21]: https://github.com/ocaml/setup-ocaml/compare/v2.0.20...v2.0.21
 [2.0.20]: https://github.com/ocaml/setup-ocaml/compare/v2.0.19...v2.0.20