fix Dockerfile?

Change-Id: I5cd133f9de490340a958403c06ab1c8c44017001
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/223186
Commit-Queue: Mike Klein <mtklein@google.com>
Reviewed-by: Ben Wagner aka dogben <benjaminwagner@google.com>
1 file changed