[infra] Upgrade iOS builders.

Change-Id: I13f402438825b2251a9149995d5c61b14f2e08a3
Reviewed-on: https://skia-review.googlesource.com/148122
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
2 files changed