Use HTTPS URL for Debian repository
Use HTTPS URL for Debian repository

With this change, Debian packages are downloaded over HTTPS. On Debian
stretch and earlier this requires installation of the
[apt-transport-https](https://packages.debian.org/stretch/apt-transport-https)
package. Debian buster and later provide apt≥1.5 which has built-in
support for HTTPS repositories.

Frost/rcm,Frost/rcm,thoughtbot/rcm,Frost/rcm,thoughtbot/rcm,Frost/rcm,thoughtbot/rcm