Using the bundler via API doesn't terminate all workers #1723 (#1760)

packages/core/parcel-bundler/src/Bundler.js

@@ -329,7 +329,7 @@ class Bundler extends EventEmitter {
 
       // If not in watch mode, stop the worker farm so we don't keep the process running.
       if (!this.watcher && this.options.killWorkers) {
-        this.stop();
+        await this.stop();
       }
     }
   }