Turn on sourcemaps flag for babel

README.md

@@ -154,7 +154,7 @@ Now we can remove the duplicated options from our npm scripts
 ```diff
   "scripts": {
 +   "start": "nodemon lib/index.js --exec babel-node",
-+   "build": "babel lib -d dist",
++   "build": "babel lib -d dist -s",
     "serve": "node dist/index.js"
   }
 ```

lib/index.js

@@ -1,3 +1,4 @@
+import 'source-map-support/register';
 import http from 'http';
 
 http.createServer((req, res) => {

package.json

@@ -5,7 +5,7 @@
   "main": "lib/index.js",
   "scripts": {
     "start": "nodemon lib/index.js --exec babel-node --presets es2015,stage-2",
-    "build": "babel lib -d dist",
+    "build": "babel lib -d dist -s",
     "serve": "node dist/index.js",
     "test": "mocha --compilers js:babel-register"
   },