Use HTTPS, not HTTP, in install scripts

Summary:
Via HackerOne. A researcher correctly reports that our install scripts use HTTP, not HTTPS, to fetch resources and execute them as root, which is a potentially significant vulnerability.

Instead, use HTTPS.

Test Plan: Verified that these URIs function correctly over HTTPS.

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D16958