fixed no tilesource defined error when using local mbtiles file

src/Mapscii.js

@@ -45,16 +45,16 @@ class Mapscii {
       this._initKeyboard();
       this._initMouse();
     }
-    this._initTileSource();
+    await this._initTileSource();
     this._initRenderer();
     this._draw();
     this.notify('Welcome to MapSCII! Use your cursors to navigate, a/z to zoom, q to quit.');
   }
 
 
-  _initTileSource() {
+  async _initTileSource() {
     this.tileSource = new TileSource();
-    this.tileSource.init(config.source);
+    await this.tileSource.init(config.source);
   }
 
   _initKeyboard() {

src/TileSource.js

@@ -31,7 +31,7 @@ const modes = {
 };
 
 class TileSource {
-  init(source) {
+  async init(source) {
     this.source = source;
     
     this.cache = {};
@@ -55,7 +55,7 @@ class TileSource {
       }
 
       this.mode = modes.MBTiles;
-      this.loadMBTiles(source);
+      await this.loadMBTiles(source);
     } else {
       throw new Error('source type isn\'t supported yet');
     }