experimental/documentation/gerrit.md: fix markdown

https://skia.googlesource.com/skia/+/master/experimental/documentation/gerrit.md

NOTRY=true
Change-Id: Id7fcb90c563dfb7cd160421d18ae84fd442eb98e
Reviewed-on: https://skia-review.googlesource.com/7752
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
1 file changed