Set NextJS build to serverless

We must build our NextJS app as a serverless app. When we build, this 
creates a standalone .js function for each page. Our NextRouter Netlify 
function can then trigger that function when a user requests a certain 
page.

Author: FinnWoelm

next.config.js

@@ -0,0 +1,6 @@
+module.exports = {
+  // Target must be serverless
+  target: 'serverless',
+  // distDir already has .next as default
+  distDir: '.next',
+};