ci/travis: fix 10.11 and 10.10 xcode images version
ci/travis: fix 10.11 and 10.10 xcode images version

- Retiring some OS X images
  https://blog.travis-ci.com/2016-11-17-retiring-some-osx-images

Signed-off-by: Koichi Shiraishi <2e5bdfebde234ed3509bcfc18121c70b6631e207@gmail.com>

go-fsnotify/fsevents,fsnotify/fsevents