feat: add express server to serve React build and update blockchain utility for token approval

server.js

@@ -0,0 +1,12 @@
+const express = require('express');
+const path = require('path');
+
+const app = express();
+app.use(express.static(path.join(__dirname, 'build')));
+app.use((req, res) => {
+  res.sendFile(path.join(__dirname, 'build', 'index.html'));
+});
+
+app.listen(3000, () => {
+  console.log('React build serving on 3000');
+});