modify: fix some codes pointed by eslint

lib/finder-app.js

@@ -1,13 +1,10 @@
 const electron = require('electron')
 const app = electron.app
 
-var finderWindow = null
-
 app.on('ready', function () {
   if (process.platform === 'darwin') {
     app.dock.hide()
   }
-  finderWindow = require('./finder-window')
 })
 
 module.exports = app