auto read electron version from package.json.

app/package.json

@@ -18,4 +18,4 @@
     "node-notifier": "^5.3.0",
     "request": "^2.87.0"
   }
-}
+}

app/version.js

@@ -1 +1 @@
-exports.version = [3,3,13,5384];
+exports.version = [3,3,13,5386];

gulpfile.js

@@ -11,7 +11,7 @@
  * 也可手动从 https://github.com/electron/electron/releases 下载最新版本，放到 ~/.electron 目录下
  * 淘宝镜像：https://npm.taobao.org/mirrors/electron/
  */
-const ELECTRON_VERSION = '3.1.8'
+const ELECTRON_VERSION = require('./package.json').devDependencies.electron.replace(/\^/, '')
 
 const fs = require('fs')
 const path = require('path')