Don't purge CSS in base and component layers

The production build was purging input[type=text] styles, because it
couldn't find it in the Rails templates. Change config, so it only
purges utility classes.

app/javascript/stylesheets/tailwind.config.js

@@ -1,11 +1,14 @@
 const defaultTheme = require('tailwindcss/defaultTheme')
 
 module.exports = {
-  purge: [
-    "./app/**/*.html.erb",
-    "./app/helpers/**/*.rb",
-    "./app/javascript/**/*.js"
-  ],
+  purge: {
+    layers: ['utilities'],
+    content: [
+      "./app/**/*.html.erb",
+      "./app/helpers/**/*.rb",
+      "./app/javascript/**/*.js"
+    ]
+  },
   darkMode: false, // or 'media' or 'class'
   theme: {
     extend: {