Add Netlify to CORS_ORIGIN_WHITELIST

From https://github.com/coala/devops/issues/90

https://app.netlify.com/sites/coala-io deploys to site https://*coala-io.netlify.com

Example is https://5a111572df99530c085408d5--coala-io.netlify.com/

These need to be added to https://gitlab.com/coala/landing/blob/master/backend/coala_web/settings.py#L140