Add stylesheets path to content list (#53)

Without this patch if you change a stylesheets file such as your
application.tailwind.css it wasn't getting picked up as changed.

Author: nickjj

lib/install/tailwind/tailwind.config.js

@@ -2,6 +2,7 @@ module.exports = {
   content: [
     './app/views/**/*.html.erb',
     './app/helpers/**/*.rb',
+    './app/assets/stylesheets/**/*.css',
     './app/javascript/**/*.js'
   ]
 }