"signatures" did not exist on "6c02ed2ffdde639807ca3de74f3c2581842e0ef5"
Update documentation to note Ruby 2.5 requirement
Update the documented version requirement of Ruby inside of Upgrading from Source to show GitLab 11.6+ needs Ruby 2.5
Update the documented version requirement of Ruby inside of Upgrading from Source to show GitLab 11.6+ needs Ruby 2.5