fix(template/background): Comment out installVueDevtools import in electron v6 (#603)

Author: AssetKid

generator/templates/base/src/background.js

@@ -3,7 +3,7 @@
 import { app, protocol, BrowserWindow } from 'electron'
 import {
   createProtocol,
-  installVueDevtools
+  <% if (devtoolsExtensionsBroken) { %>/* installVueDevtools */<% } else { %>installVueDevtools<% } %>
 } from 'vue-cli-plugin-electron-builder/lib'
 const isDevelopment = process.env.NODE_ENV !== 'production'