Bump travis to using Xcode 11.1.
Bump travis to using Xcode 11.1.

google/google-api-objectivec-client-for-rest,google/google-api-objectivec-client-for-rest,google/google-api-objectivec-client-for-rest,google/google-api-objectivec-client-for-rest,google/google-api-objectivec-client-for-rest