Update to Tailwind CSS v3.1.8

I need the fix in tailwindlabs/tailwindcss#8687 which was release in v3.1.4.

Has there been any thought in decoupling `tailwindcss-rails` releases from Tailwind? It would be nice to be able to use the latest Tailwind release without having to wait for `tailwindcss-rails` to be released.

Author: TastyPi

lib/tailwindcss/upstream.rb

@@ -1,7 +1,7 @@
 module Tailwindcss
   # constants describing the upstream tailwindcss project
   module Upstream
-    VERSION = "v3.1.3"
+    VERSION = "v3.1.8"
 
     # rubygems platform name => upstream release filename
     NATIVE_PLATFORMS = {