Style guide fixes

Author: nt1m

manifest.json

@@ -36,6 +36,6 @@
     "default_title": "Subscribe",
     "default_popup": "popup/popup.html"
   },
-  "permissions": [ "storage", "bookmarks", "history", "notifications", "<all_urls>", "tabs", "menus" ],
+  "permissions": ["storage", "bookmarks", "history", "notifications", "<all_urls>", "tabs", "menus"],
   "version": "1.1"
 }

shared/feed-parser.js

@@ -4,7 +4,7 @@
 const FeedParser = {
   fetchXML(url) {
     return new Promise((resolve, reject) => {
-      let request = new XMLHttpRequest();
+      const request = new XMLHttpRequest();
       request.open("GET", url, true);
 
       request.addEventListener("load", (event) => {