升级gulp到v4

[holyzfy]

1. 如果之前全局安装过gulp的v3版本，请先删除 npm uninstall -g gulp
2. 在febu目录运行 git pull && npm install

如果提示类似这样的错误，请按说明删掉相应的文件后重试

/usr/local/bin/gulp -> /usr/local/lib/node_modules/gulp-cli/bin/gulp.js
npm ERR! Darwin 14.5.0
npm ERR! argv "/usr/local/bin/node" "/usr/local/bin/npm" "install" "-g" "gulp-cli"
npm ERR! node v6.2.2
npm ERR! npm  v3.9.5
npm ERR! path /usr/local/share/man/man1/gulp.1
npm ERR! code EEXIST

npm ERR! Refusing to delete /usr/local/share/man/man1/gulp.1: ../../../lib/node_modules/gulp/gulp.1 symlink target is not controlled by npm /usr/local
npm ERR! File exists: /usr/local/share/man/man1/gulp.1
npm ERR! Move it away, and try again.