TensorFlow: use xcode 10.2.1
There is a Apple Clang issue in Xcode 11 that causes protoc to crash if it's compiled with certain options, we have to switch back to  Xcode 10 until this is resolved.
@@ -24,6 +24,7 @@ platforms:
environment:
TF_IGNORE_MAX_BAZEL_VERSION: 1
USE_BAZEL_VERSION: latest
+ xcode_version: "10.2.1"
shell_commands:
# - |-
# echo '
