Roll external/skia 18f960209..783c43658 (1 commits)

https://skia.googlesource.com/skia.git/+log/18f960209..783c43658

2017-05-04 egdaniel@google.com Fix comma in vulkan

Test: Presubmit checks will test this change.
Change-Id: Id859bae1eeb9d206789f21ddc255c14195b17b23