Update heroku/buildpacks-ruby to v2.1.0 (#395)

## heroku/ruby

### Added

- Introduce heroku build metrics support (heroku/buildpacks-ruby#172)
- Changelog moved to be per-crate rather than for the whole project (heroku/buildpacks-ruby#154)

Co-authored-by: heroku-linguist[bot] <136119646+heroku-linguist[bot]@users.noreply.github.com>

builder-20/builder.toml

@@ -34,7 +34,7 @@ version = "0.17.1"
 
 [[buildpacks]]
   id = "heroku/ruby"
-  uri = "docker://docker.io/heroku/buildpack-ruby@sha256:fd32f123fdfa3e94eeb4ce2ad82aad353f6a3b87ac70bfebfdd30cc41927a737"
+  uri = "docker://docker.io/heroku/buildpack-ruby@sha256:c4f5df18845ebd3a72be17699de63ec9afb784915fe357a8a30854d0dc61631d"
 
 [[buildpacks]]
   id = "heroku/scala"
@@ -64,7 +64,7 @@ version = "0.17.1"
     optional = true
   [[order.group]]
     id = "heroku/ruby"
-    version = "2.0.1"
+    version = "2.1.0"
   [[order.group]]
     id = "heroku/procfile"
     version = "2.0.1"

builder-22/builder.toml

@@ -42,7 +42,7 @@ version = "0.17.1"
 
 [[buildpacks]]
   id = "heroku/ruby"
-  uri = "docker://docker.io/heroku/buildpack-ruby@sha256:fd32f123fdfa3e94eeb4ce2ad82aad353f6a3b87ac70bfebfdd30cc41927a737"
+  uri = "docker://docker.io/heroku/buildpack-ruby@sha256:c4f5df18845ebd3a72be17699de63ec9afb784915fe357a8a30854d0dc61631d"
 
 [[buildpacks]]
   id = "heroku/scala"
@@ -72,7 +72,7 @@ version = "0.17.1"
     optional = true
   [[order.group]]
     id = "heroku/ruby"
-    version = "2.0.1"
+    version = "2.1.0"
   [[order.group]]
     id = "heroku/procfile"
     version = "2.0.1"