Update sapper example to use correct config file name

Author: adamwathan

examples/sapper/postcss.config.js

@@ -1,5 +1,3 @@
-const tailwindcss = require("tailwindcss");
-
 // only needed if you want to purge
 const purgecss = require("@fullhuman/postcss-purgecss")({
   content: ["./src/**/*.svelte", "./src/**/*.html"],
@@ -8,7 +6,7 @@ const purgecss = require("@fullhuman/postcss-purgecss")({
 
 module.exports = {
   plugins: [
-    tailwindcss("./tailwind.js"),
+    require("tailwindcss"),
 
     // only needed if you want to purge
     ...(process.env.NODE_ENV === "production" ? [purgecss] : [])