The problem is that Uglify mangles too much by default in your case. As per bitcoinjs-lib instructions, you need to exclude certain names like this:
plugins: [
    new webpack.optimize.UglifyJsPlugin({
        mangle: {
            except: [
                'Array', 'BigInteger', 'Boolean', 'Buffer',
                'ECPair', 'Function', 'Number', 'Point'
            ]
        }
    })
]
Use webpack instead of webpack -p after configuring the plugin.
It will work.