Don't use async within describe

src/TileSource.spec.js

@@ -2,10 +2,10 @@
 const TileSource = require('./TileSource');
 
 describe('TileSource', () => {
-  describe('with a HTTP source', async () => {
+  describe('with a HTTP source', () => {
+    test('sets the mode to 3', async () => {
       const tileSource = new TileSource();
       await tileSource.init('http://mapscii.me/');
-    test('sets the mode to 3', () => {
       tileSource.mode = 3;
     });
   });