fix rackup server deprecated message

Procfile.dev

@@ -1,3 +1,3 @@
 # web: env RUBY_DEBUG_OPEN=true bin/rails server --port 3000
 web: env TERMINAL_PREFIX=15 bin/rails server --port 3000
-css: bin/rails tailwindcss:watch
+css: bin/rake tailwindcss:watch

bin/rake

@@ -1,4 +1,9 @@
 #!/usr/bin/env ruby
-require_relative "../config/boot"
-require "rake"
+require_relative '../config/boot'
+require 'rake'
+require 'rackup'
+module Rack
+  Handler = ::Rackup::Handler
+end
+
 Rake.application.run