Remove will-change property

[robmaurizi]

Including will-change on .glide__slides introduces a rendering issue in Safari when a slide contains a video and the user tries to watch said video in full screen. Removing this one property (or defaulting it to auto) resolves the issue.

See https://codepen.io/robmaurizi-the-vuer/full/rNJpPON for an example of the offending behavior.

This resolves https://github.com/glidejs/glide/issues/616