Referrer is being sent to jsdelivr

[michaelgmiller]

In https://github.com/graphql-python/flask-graphql/blob/master/flask_graphql/render_graphiql.py#L24, the referrer is being sent on the static assets. This is problematic for large queries

[michaelgmiller]

@syrusakbary Thanks for merging quickly! Any chance of a release to incorporate this?