TLS Links for Improved Security

[justinormont]

For general web security, we should use HTTPS links instead of HTTP.

Within the ML.NET repo, I see ~76 locations where we use HTTP:
https://github.com/Microsoft/NimbusML/search?p=3&q=http%3A%2F%2F&unscoped_q=http%3A%2F%2F

Task:

• Verify that HTTPS links are equivalent
• Where possible, change links to utilize HTTPS

Issue #52 / PR #56 handles this for scikit-learn, this is a more general task.

[skasturi]

Still need to verify that the links work. Will do that over the weekend.

Quick PR for this: #98