text: Title: Replace use of websocketbridge.js
  Body: The underlying `channels` library has a backwards-incompatible change in v2.1.4 - the file `websocketbridge.js` was removed.
  
  The workaround is to require v2.1.3 of this package, but a better fix is to replace the use of websocketbridge.js in the messaging [template](https://github.com/GibbsConsulting/django-plotly-dash/blob/master/django_plotly_dash/templates/django_plotly_dash/plotly_messaging.html).