Rename MRSK to Kamal

https://github.com/basecamp/kamal/releases/tag/v0.16.0

[ci skip]

Author: morgoth

railties/lib/rails/generators/app_base.rb

@@ -554,7 +554,7 @@ def dockerfile_build_packages
       end
 
       def dockerfile_deploy_packages
-        # Add curl to work with the default healthcheck strategy in MRSK
+        # Add curl to work with the default healthcheck strategy in Kamal
         packages = ["curl"]
 
         # ActiveRecord databases