Fix app update for marathon 1.4.x

Since Marathon 1.4.x, it seems that app versions are not returned in a
specific order, but some of the logic in marathon-ui relies on it. This
is fixed by sorting the versions list received in descending order, as
it was returned by previous Marathon versions.

src/js/stores/AppVersionsStore.js

@@ -41,7 +41,16 @@ var AppVersionsStore = Util.extendObject(EventEmitter.prototype, {
 
   getAppVersions: function (appId) {
     if (appId === storeData.currentAppId) {
-      return this.availableAppVersions;
+      return this.availableAppVersions
+        .sort(function (a, b) {
+          if (a < b) {
+            return 1;
+          }
+          if (a > b) {
+            return -1;
+          }
+          return 0;
+        });
     }
     return [];
   },