Fix test errors caused by upgrade in Chai dependency

Author: jakezatecky

test/setup.js

@@ -12,6 +12,7 @@ function copyProps(src, target) {
 
 global.window = window;
 global.document = window.document;
+global.HTMLElement = window.HTMLElement;
 global.navigator = {
     userAgent: 'node.js',
 };