ensure no buildroot macro left in /usr/bin/docker
    
    A new change soon to be merged upstream will leave the buildroot macro
    in /usr/bin/docker in the rpmbuild process.
    
    This commit will sanitize the buildroot macro from /usr/bin/docker.
    
    Signed-off-by: Lokesh Mandvekar <lsm5@fedoraproject.org>