hide dock icon if window closes

app/src/index.ts

@@ -78,6 +78,11 @@ function firstRunWindow() {
 
   welcomeWindow.loadURL(MAIN_WINDOW_WEBPACK_ENTRY)
   welcomeWindow.on('ready-to-show', () => welcomeWindow.show())
+  welcomeWindow.on('closed', () => {
+    if (process.platform === 'darwin') {
+      app.dock.hide()
+    }
+  })
 }
 
 let tray: Tray | null = null