[Travis] Use default Ruby
[Travis] CocoaPods requires the terminal to be using UTF-8 encoding.
[Travis] Export LANG before cocoapods install
[Travis] Invoke xctool manually
[Travis] Update xctool before running the tests

See https://github.com/travis-ci/travis-ci/issues/2179
[Travis] Remove .xctool-args
Merge branch 'travis'