[INFO] cloning repository https://github.com/cis198-2016f/shell-workshop
[INFO] running `Command { std: "git" "-c" "credential.helper=" "-c" "credential.helper=/workspace/cargo-home/bin/git-credential-null" "clone" "--bare" "https://github.com/cis198-2016f/shell-workshop" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fcis198-2016f%2Fshell-workshop", kill_on_drop: false }`
[INFO] [stderr] Cloning into bare repository '/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fcis198-2016f%2Fshell-workshop'...
[INFO] running `Command { std: "git" "rev-parse" "HEAD", kill_on_drop: false }`
[INFO] [stdout] 8e19147715ee3e1df4be8701dfcb0e7cc34eb51d
[INFO] checking cis198-2016f/shell-workshop against master#040e2f8b9ff2d76fbe2146d6003e297ed4532088 for pr-143619
[INFO] running `Command { std: "git" "clone" "/workspace/cache/git-repos/https%3A%2F%2Fgithub.com%2Fcis198-2016f%2Fshell-workshop" "/workspace/builds/worker-6-tc1/source", kill_on_drop: false }`
[INFO] [stderr] Cloning into '/workspace/builds/worker-6-tc1/source'...
[INFO] [stderr] done.
[INFO] [stderr] fatal: update_ref failed for ref 'HEAD': cannot update ref 'refs/heads/master': couldn't write '/workspace/builds/worker-6-tc1/source/.git/refs/heads/master.lock'


failed to checkout https://github.com/cis198-2016f/shell-workshop

Caused by:
    command failed: exit status: 128