run eslint to fix most var instances

src/scripts/multiDownload.js

@@ -1,10 +1,10 @@
 import browser from 'browser';
 
 function fallback(urls) {
-    var i = 0;
+    let i = 0;
 
     (function createIframe() {
-        var frame = document.createElement('iframe');
+        const frame = document.createElement('iframe');
         frame.style.display = 'none';
         frame.src = urls[i++];
         document.documentElement.appendChild(frame);
@@ -28,14 +28,14 @@ function fallback(urls) {
 }
 
 function sameDomain(url) {
-    var a = document.createElement('a');
+    const a = document.createElement('a');
     a.href = url;
 
     return window.location.hostname === a.hostname && window.location.protocol === a.protocol;
 }
 
 function download(url) {
-    var a = document.createElement('a');
+    const a = document.createElement('a');
     a.download = '';
     a.href = url;
     // firefox doesn't support `a.click()`...
@@ -51,7 +51,7 @@ export default function (urls) {
         return fallback(urls);
     }
 
-    var delay = 0;
+    let delay = 0;
 
     urls.forEach(function (url) {
         // the download init has to be sequential for firefox if the urls are not on the same domain