Correct proxy usage docs (#7368)

Author: szabolcs-szilagyi

docusaurus/docs/proxying-api-requests-in-development.md

@@ -96,7 +96,10 @@ You can now register proxies as you wish! Here's an example using the above `htt
 const proxy = require('http-proxy-middleware');
 
 module.exports = function(app) {
-  app.use(proxy('/api', { target: 'http://localhost:5000/' }));
+  app.use('/api', proxy({
+    target: 'http://localhost:5000',
+    changeOrigin: true,
+  }));
 };
 ```