make recipes work with next-compose-plugins

[biowaffeln]

Currently recipes like MDX and Preact that update next.config.js don't work if the existing config uses next-compose-plugins. Plugins should be inserted like this:

// next.config.js
const withPlugins = require('next-compose-plugins');

module.exports = withPlugins(
  [ /* insert plugin here */ ],
  { /* insert config here */ }
);