Add exit menu item

src/menu.js

@@ -37,6 +37,12 @@ module.exports = (app, mainWindow, newVersion) => {
           mainWindow.webContents.send('html5ify', true);
         },
       },
+      {
+        label: 'Exit',
+        click() {
+          app.quit();
+        },
+      },
     ],
   });