Use official Redshift driver in docs

[Brooke-white]

Hi there, I maintain redshift_connector.

I noticed https://github.com/plotly/graphing-library-docs/blob/master/_posts/python-v3/databases/redshift.ipynb uses psycopg2. redshift_connector is mentioned here on the plotly website, but this example uses psycopg2. Could you folks consider updating this to use redshift_connector?

redshift_connector supports integration with SQLAlchemy via the Redshift specific SQLAlchemy dialect (sqlalchemy-redshift) as well as a bunch of Redshift specific features such as IAM and Identity provider based authentication as well as support for Redshift native datatypes.