some changes

hello.js

@@ -0,0 +1,13 @@
+module.exports = function (req, res, next) {
+  var userName = req.body.user_name;
+  var botPayload = {
+    text : 'Hello, ' + userName + '!'
+  };
+
+  // avoid infinite loop
+  if (userName !== 'slackbot') {
+    return res.status(200).json(botPayload);
+  } else {
+    return res.status(200).end();
+  }
+}