Fix public API msg in PRESUBMIT.py

BUG=skia:5825

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2989

Change-Id: Ia074ab00ccd1500bee10a5b313636581e8265461
Reviewed-on: https://skia-review.googlesource.com/2989
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
1 file changed