Fix ci builder

[jingwei-huang1]

• [x] Remove iOS 9.3 simulators for tests to fix broken CI build
• [x] Investigate why the build still passes with an error
• [ ] Investigate how to enable iOS 9.3 simulator

[staguer]

I asked on https://github.com/travis-ci/docs-travis-ci-com/issues/1106 about 9.3 being gone. I wonder if there's a better place for that.