Add graphiz to doxygen/Dockerfile
Add graphiz to doxygen/Dockerfile

See context in https://bugs.chromium.org/p/skia/issues/detail?id=13020#c1

Bug: skia:13020
Change-Id: If0bdf728b29d952e3066ea575b493961c9c9a0fe
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/515852
Reviewed-by: Joe Gregorio <b9cf2471ff6d33504cafe8e6f356b732b2cadced@google.com>
Commit-Queue: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot