add X-FORWARDED headers for proxy requests (facebook#1677)

Author: johann-sonntagbauer

packages/react-scripts/scripts/start.js

@@ -214,7 +214,8 @@ function addMiddleware(devServer) {
       onError: onProxyError(proxy),
       secure: false,
       changeOrigin: true,
-      ws: true
+      ws: true,
+      xfwd: true
     });
     devServer.use(mayProxy, hpm);