experimental/documentation/gerrit.md: check for error case

NOTRY=true
Change-Id: I0eebe482111efa90dc2fb9d106bdacaf689a38d3
Reviewed-on: https://skia-review.googlesource.com/21371
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed