Prepare release v3.1.1

## heroku/procfile

- No changes.

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [3.1.1] - 2024-05-02
+
+- No changes.
+
 ## [3.1.0] - 2024-05-02
 
 ### Added
@@ -81,7 +85,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Initial release of Rust procfile buildpack, the old Go buildpack is now archived.
 - Re-write logic of Procfile parsing to match Heroku's behavior, which has different behavior from the Go version (that assumed that a Procfile was YAML syntax).
 
-[unreleased]: https://github.com/heroku/buildpacks-procfile/compare/v3.1.0...HEAD
+[unreleased]: https://github.com/heroku/buildpacks-procfile/compare/v3.1.1...HEAD
+[3.1.1]: https://github.com/heroku/buildpacks-procfile/compare/v3.1.0...v3.1.1
 [3.1.0]: https://github.com/heroku/buildpacks-procfile/compare/v3.0.1...v3.1.0
 [3.0.1]: https://github.com/heroku/buildpacks-procfile/compare/v3.0.0...v3.0.1
 [3.0.0]: https://github.com/heroku/buildpacks-procfile/compare/v2.0.2...v3.0.0

buildpack.toml

@@ -2,7 +2,7 @@ api = "0.10"
 
 [buildpack]
 id = "heroku/procfile"
-version = "3.1.0"
+version = "3.1.1"
 name = "Heroku Procfile"
 homepage = "https://github.com/heroku/buildpacks-procfile"
 description = "Heroku's Procfile buildpack."