mac系统image-webpack-loader压缩图片一直报错

一堆这样的错误：node_modules/pngquant-bin/vendor/pngquant ENOENT

node_modules/mozjpeg/vendor/cjpeg ENOENT

上网查找解决办法，然后安装libpng

$ brew install libpng

Updating Homebrew...

^CWarning: libpng 1.6.34 is already installed

安装后还是继续报同样的错误，怎么办

注：我的代码：

{

test: /\.(png|jpg|svg|gif)$/i,

loaders: [

'url-loader?limit=20000&name=[name]-[hash:5].[ext]',

'image-webpack-loader'

]

}