Revert "use Xcode 8.2 in travis environment."
Revert "use Xcode 8.2 in travis environment."

This reverts commit 3a0673e8edc0616872788893013894ad4272cc39.

simonracz/detox,simonracz/detox,simonracz/detox,simonracz/detox,simonracz/detox