Fix readme

Author: npezza93

README.md

@@ -174,7 +174,7 @@ The inline version also works:
 ## Puma plugin
 We provide a Puma plugin if you want to run the Tailwind watcher together with Puma and have Puma monitor and manage it. You just need to add
 ```ruby
-plugin :tailwindcss if Rails.env.development?
+plugin :tailwindcss if ENV.fetch("RAILS_ENV", "development") == "development"
 ```
 to your `puma.rb` configuration.