[refactor] Update entry point in webpack configuration (#586)

Following #583.

Author: darrachequesne

support/webpack.config.js

@@ -1,6 +1,6 @@
 
 module.exports = {
-  entry: './index.js',
+  entry: './lib/index.js',
   output: {
     filename: 'engine.io.js',
     library: 'eio',