http -> https and URL update

[ViralBShah]

Redirect the http to https for the computationalthinking.mit.edu URL. Or click "Enforce HTTPS" in settings.

Also, update the URL for the class on the repo.

cc @christopher-dG

[christopher-dG]

@shashi took care of the checkbox, and the URLs too I think (although there's a typo in website-docs.md: computationalthinking.mit.edut/Fall20 which should be https://computationalthinking.mit.edu/Fall20)

[christopher-dG]

The URL in the repo settings could be updated though.