Unnecessary focus/blur on keyup.

[patricknelson]

Net result is that attempting to use the spacebar to open the drop-down in IE 11 will fail, as the menu displays and disappears immediately. I believe this is a legacy of the following old commit:
9ba52e9

The current code is located here, so this should be removed (linking to specific commit for posterity since this repo hasn't been updated in ages):

jquery.customSelect/jquery.customSelect.js

Line 107 in 6af8d15

$select.trigger('blur.customSelect');