Map does not resize as claimed

[6zz]

Create a map and call it by the div where you want it, it will automatically size to fit the div. It will also resize when the window resizes, to deal with dynamically sized divs.

In the getting started section, this above claims the created map would resize when the window resizes, but the example, does not support that claim. I have ported the example to codepen (http://codepen.io/szz/pen/EWqqBL/) to try out the resizing...