docs(README): link to webpack 2 docs (#72)

Author: simon04

README.md

@@ -19,9 +19,7 @@
 npm install --save-dev url-loader
 ```
 
-<h2 align="center">Usage</h2>
-
-[Documentation: Using loaders](http://webpack.github.io/docs/using-loaders.html)
+<h2 align="center"><a href="https://webpack.js.org/concepts/loaders">Usage</a></h2>
 
 The `url` loader works like the `file` loader, but can return a Data Url if the file is smaller than a byte limit.