Build file not updating in Node.js

So I am building a react application. The application works fine in development instance. But when I try to open the final output file, the file doesn't update.

Example - I made a Hello app in React. Now, I am working in react-bootstrap. But the final output file still shows Hello.

This is my webpack.config.js file

var HTMLWebpackPlugin = require('html-webpack-plugin');
var HTMLWebpackPluginConfig = new HTMLWebpackPlugin({
    template: __dirname + '/app/index.html',    
    filename: 'index.html',
    inject: 'body'
});

module.exports = {

    entry: __dirname + '/app/index.js',
    module: {
        loaders: [
            {
                test: /\.js$/,
                exclude: /node_modules/,
                loader: 'babel-loader'
            },
            { 
                test: /\.css$/, 
                loader: "style-loader!css-loader" 
              },


        ]
    },

    output: {
        filename: 'transformed.js',
        path: __dirname+'/build'
    },
    plugins: [HTMLWebpackPluginConfig]
};

Can't understand where the error lies. Please help :)

via Ciedzs