Collapsible laten werken met werkelijke hoogte van in te klappen element

	var coll = document.getElementsByClassName("collapsible");
	var i;
	for (i = 0; i < coll.length; i++) {
		coll[i].addEventListener("click", function() {
			var content = this.nextElementSibling;
			content.classList.toggle("inactive");
			if(content.classList.contains("inactive")){
				content.style.maxHeight = null;
			}else{
				content.style.maxHeight = content.scrollHeight + "px";
			}
		});
	}