Upgrade link to use HTTPS
Upgrade link to use HTTPS

This one displays a mixed-content warnings, that is why we
decided to commit it apart. It works though and is probably
better than no HTTPS at all.

Co-Authored-By: Keegan Helmbrecht <caa5d918428bea6fc9e58ff827b016762bf5619d@gmail.com>

conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop,conorsch/securedrop