替换一下这个，试试

{
    test: /\.css$/,
    use: [//loader解析顺序：先postcss->然后css->最后style-loader
        'style-loader',
        {
            loader: 'css-loader',
            options: {importLoaders: 1}
        },//importLoaders默认是0，意思是一个加载器都不用，
        // 1:用postcss-loader加载器处理，
        // 2:用postcss-loaders和sass-loader加载器处理
        {
            loader: "postcss-loader",
            options: {
                plugins: [
                    require("autoprefixer")({//自动增加浏览器前缀(-webkit-等)
                        browsers: ['last 5 versions']
                    })
                ]
            }
        }
    ]
}