Change git protocol to https protocol in Gemfile for GitLab 5.0

Changes gems to use https protocol rather than the git protocol for GitLab 5.0 release. Git protocol does not work behind some firewalls and/or proxies. This change helps users upgrading from 4.2 to 7.1 have a smoother upgrade process. Fixes https://github.com/gitlabhq/gitlabhq/issues/3416 & https://github.com/gitlabhq/gitlabhq/issues/3478.