improve mojang status message

as Mojang has removed their status page and their status API is no longer updating,
status information is now fetched from https://mc-heads.net/json/mc_status
and the warning message links to https://mc-heads.net/mcstatus

see #271, closes #272

lib/public/javascript/crafatar.js

@@ -1,5 +1,4 @@
 var valid_user_id = /^[0-9a-f-A-F-]{32,36}$/; // uuid
-var xhr = new XMLHttpRequest();
 
 var quotes = [
   ["Crafatar is the best at what it does.", "Shotbow Network", "https://twitter.com/ShotbowNetwork/status/565201303555829762"],
@@ -37,25 +36,18 @@ function changeQuote() {
   current_quote = (current_quote + 1) % quotes.length;
 }
 
-xhr.onload = function() {
-  var response = JSON.parse(xhr.responseText);
-  var status = {};
-  response.map(function(elem) {
-    var key = Object.keys(elem)[0];
-    status[key] = elem[key];
-  });
-
-  var textures_err = status["textures.minecraft.net"] !== "green";
-  var session_err = status["sessionserver.mojang.com"] !== "green";
+fetch('https://mc-heads.net/json/mc_status').then(r => r.json()).then(data => {
+  var textures_err = data.report.skins.status !== "up";
+  var session_err = data.report.session.status !== "up";
 
   if (textures_err || session_err) {
     var warn = document.createElement("div");
     warn.setAttribute("class", "alert alert-warning");
     warn.setAttribute("role", "alert");
-    warn.innerHTML = "<h5>Mojang issues</h5> Mojang's servers are having trouble <i>right now</i>, this may affect requests at Crafatar. <small><a href=\"https://help.mojang.com\" target=\"_blank\">check status</a>";
+    warn.innerHTML = "<h5>Mojang issues</h5> Mojang's servers are having trouble <i>right now</i>, this may affect requests at Crafatar. <small><a href=\"https://mc-heads.net/mcstatus\" target=\"_blank\">check status</a>";
     document.querySelector("#alerts").appendChild(warn);
   }
-};
+});
 
 document.addEventListener("DOMContentLoaded", function(event) {
   var avatars = document.querySelector("#avatar-wrapper");
@@ -82,7 +74,4 @@ document.addEventListener("DOMContentLoaded", function(event) {
       images[j].src = images[j].dataset.src.replace("$", value);
     }
   };
-
-  xhr.open("GET", "https://status.mojang.com/check", true);
-  xhr.send();
 });