remove the sticky el from the test DOM after each test

spec/javascripts/lib/utils/sticky_spec.js

@@ -4,15 +4,19 @@ describe('sticky', () => {
   let el;
 
   beforeEach(() => {
-    document.body.innerHTML = `
+    document.body.innerHTML += `
       <div class="parent">
-        <div id="js-sticky" style="position: relative;"></div>
+        <div id="js-sticky"></div>
       </div>
     `;
 
     el = document.getElementById('js-sticky');
   });
 
+  afterEach(() => {
+    el.parentNode.remove();
+  });
+
   describe('when stuck', () => {
     it('does not remove is-stuck class', () => {
       isSticky(el, 0, el.offsetTop);