Internet Explorer 11 error "Unable to get property 'Windows' of undefined or null reference"

Very minor issue, tipboard seems to function well even with this error happening.

Error message (visible in the Internet Explorer Javascript console):

> Unable to get property 'Windows' of undefined or null reference

It occurs at this point:

https://github.com/allegro/tipboard/blob/15cb0e31acf8c8363406fd55ded4fa6a7f910814/tipboard/static/js/lib/jquery.fullscreen.js#L93

Reproduces on Internet Explorer 11.1066.14393.0

The jquery.fullscreen.js mentions that its source is http://www.quirksmode.org/js/detect.html, but it is no longer there.