gulpfile.js

gulp.task("webpack-dev-server", function() {
    // modify some webpack config options
    var myConfig = Object.create(webpackConfig);

    // Start a webpack-dev-server
    new WebpackDevServer(webpack(myConfig),{
        contentBase: 'build',
        inline:true
    })
        .listen(8080, "localhost", function(err) {
            if(err) throw new gutil.PluginError("webpack-dev-server", err);
            gutil.log("[webpack-dev-server]", "http://localhost:8080/webpack-dev-server/index.html");
        });
});

webpack.config.js

var path = require("path");
var webpack = require("webpack");

module.exports = {
    entry: {
        app: [
            './app/index.js'
        ]
    },
    output: {
        path: path.resolve(__dirname, "build"),
        publicPath: "/",
        filename: '[name].js'
    },
    devServer: {
        contentBase: 'build'
    },
    module: {
        loaders: [
            {
                test: /\.js$/,
                exclude: /node_modules/,
                loader: 'babel',
                query: {
                    presets: ['es2015', 'react'],
                    plugins: ["transform-object-assign"]
                }
            }
        ]
    },
    plugins: [

    ]
};