added es6 library

cssrefresh.js

@@ -0,0 +1,33 @@
+(function() {
+    function cssRefresh(link) {
+        let href = link.href + '?x=' + Math.random();
+
+        fetch(href, {
+            method: 'HEAD'
+        })
+        .then(response => {
+            let lastModified = new Date(response.headers.get('last-modified'));
+            if (response.ok && (lastModified > link.lastModified || !link.lastModified)) {
+                link.lastModified = lastModified;
+                link.element.setAttribute('href', href);
+            }
+
+            setTimeout(() => {
+                cssRefresh(link);
+            }, 1000);
+        })
+    }
+
+    Array.prototype.slice.call(document.querySelectorAll('link'))
+        .filter(link => link.rel === 'stylesheet' && link.href)
+        .map(link => {
+            return {
+                element: link,
+                href: link.getAttribute('href').split('?')[0],
+                lastModified: false
+            };
+        })
+        .forEach(function(link) {
+            cssRefresh(link);
+        });
+})();