[test] Fix typo in numfuzzer

NOTRY=true
TBR=sergiyb@chromium.org

Bug: chromium:830557
Change-Id: I61510297e5195eb74425c71e41c4d95f080a280d
Reviewed-on: https://chromium-review.googlesource.com/1016420Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52659}