[ci/mac] Upgrade to macOS 10.12 for build workers.
This change will cause all builds of `core/hab` on macOS to use version
10.12. Prior to this change 10.11 was used but this infrastructure was
retired within the last couple of weeks.
@@ -59,7 +59,7 @@ steps:
# they're also not being used by anyone else.
queue: omnibus
os: Darwin
- "os:version": 10.11 # Build statically on the oldest thing we can
+ "os:version": 10.12 # Build statically on the oldest thing we can
- wait
