Update references to master branch

Change-Id: I1bfd1b655af6cdfbd64452b1e594a276425095fe
Bug: skia:11987
Docs-Preview: https://skia.org/?cl=410790
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/410790
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
24 files changed