Dropdown displaced when using pinch zoom

This is reproducible in the [demo page](https://select2.org/getting-started/basic-usage). Click on the first example, and then zoom in. The dropdown will become displaced. Tested on macOS Sierra with Chrome.

![image](https://user-images.githubusercontent.com/11954789/30731632-17c0603e-9fa1-11e7-9e7c-893056174195.png)