Avoid errors resolving dependencies in GHCJS output

src/index.js

@@ -9,6 +9,16 @@ module.exports = (nextConfig = {}) => {
 
       const { dir, dev, isServer } = options;
 
+      //TODO: We need this because all.js includes conditional `require`
+      //commands for these modules; even though it does not use them in
+      //practice, webpack wants to find them statically.  Instead, we should
+      //deal with this in haskell-loader, e.g. by asking GHCJS not to produce
+      //these `require` invocations.
+      config.resolve.fallback = {
+        ...config.resolve.fallback,
+        fs: false,
+        child_process: false
+      };
       config.module.rules.push({
         test: /\.(cabal)$/,
         use: [