Viewport is not a constructor

I am trying to set a simple HTML example of pixi-viewport but a get this

Uncaught TypeError: Viewport is not a constructor

I am still using pixi V4

<!doctype html>
<html>
<head>
    <meta charset="utf-8">
    <title>Hello Pixi</title>
</head>
<script src="pixi/pixi.min.js"></script>
<script src="pixi/viewport.js"></script>
<body>
    <script type="text/javascript">
        let type = "WebGL"
        if(!PIXI.utils.isWebGLSupported()){
            type = "canvas"
        }

        //Aliases
        let Application = PIXI.Application,
            loader = PIXI.loader,
            resources = PIXI.loader.resources,
            Sprite = PIXI.Sprite;
            Graphics = PIXI.Graphics

        //Create a Pixi Application
        let app = new Application({
            width: 953,
            height: 409,
            backgroundColor: 0xFFFFFF
        });

        //Add the canvas that Pixi automatically created for you to the HTML document
        document.body.appendChild(app.view);

        const viewport = new Viewport({
            screenWidth: window.innerWidth,
            screenHeight: window.innerHeight,
            worldWidth: 1000,
            worldHeight: 1000,

            interaction: app.renderer.plugins.interaction // the interaction module is important for wheel to work properly when renderer.view is placed or scaled
        })

    </script>
</body>
</html>

davidfig / pixi-viewport

Viewport is not a constructor #230