[j0hnik]

<script src="https://code.jquery.com/jquery-3.3.1.min.js"></script>
	<form class="filter">
	<div class="filter-group">				
	<select name="filter">				 
	  <option value="services-slide_one">Все</option>
	  <option value="evac">Эвакуатор</option>
	  <option value="gruz">Грузоперевозки</option>				
	</select>
	 </div>
</form>
	<script>	

$('select').on('change', function () {
	document.body.className = this.value;
});

	</script>

или точки уберите