Flatpickr with Spectre: Icons broken

[eduo]

Hi.

I've noticed that Flatpickr integration tries to use the current icon handling when using different libraries (for example, when using fontawesome or bootstrap it will change the labels accordingly) but for Spectre it seems to be broken.

Example (it's the standard Flatpickr example, but the library was changed to Spectre): https://is.gd/lLz069

As you can see, the icons are wrong:

The normal look would be this for fontawesome 3:

It should be noted that the icons seem to be broken also in JQuery UI and bootstrap 3, whereas in Bootstrap 2 they revert to text

It currently maps to icon-bookmark and icon-close to represent a calendar popup and a way to close the calendar, but for Spectre I'd recommend using icon-edit or icon-resize-vert to popup the calendar and icon-cross or for the second. Alternatively icon-plus and icon-minus could be used.

Since I'm loading via CDN, I can't override these. I was surprised they had never been reported either.