Make the !source command output more saucy

2 jobs for master in 6 seconds (queued for 40 seconds)
Name Stage Failure
test Test
   9a1cbcb..379f0f2  master     -> origin/master
Checking out 379f0f2c as master...
Skipping Git submodules setup
Checking cache for default...
time="2020-05-26T21:51:39+08:00" level=error msg="Docker executor: prebuilt image helpers will be loaded from /var/lib/gitlab-runner."
Successfully extracted cache
$ rustc --version
bash: line 80: rustc: command not found
ERROR: Job failed: exit status 1