Use HEAD instead of @ shortcut for git in launcher (#428)
Use HEAD instead of @ shortcut for git in launcher (#428)

The abbreviation @ for HEAD was added in git 1.8.5. The launcher claims to be compatible with git version 1.8.0 but the use of this abbreviation breaks this compatibility. This change is needed to support RHEL 7.6 which has only git 1.8.3.1.
discourse/discourse_docker,discourse/discourse_docker,discourse/discourse_docker