Restore window on activate event

main.js

@@ -16,6 +16,14 @@ app.on('window-all-closed', function() {
   }
 });
 
+app.on('activate', function () {
+  // On OS X it's common to re-create a window in the app when the
+  // dock icon is clicked and there are no other windows open.
+  if (mainWindow === null) {
+    app.emit('ready');
+  }
+});
+
 // This method will be called when Electron has finished
 // initialization and is ready to create browser windows.
 app.on('ready', function() {