Hint for those who live outside USA - jenkins understands only en_US.UTF-8
If (like me) you get jenkins error “invalid byte sequence in US-ASCII (ArgumentError)”
Try to export language before fastlane command, so the build command (Project Configure->Build->Command) looks like this:
Small ambiguity - in .travis.yml file it’s osx_image: xcode10.1 but the tutorial mentions Xcode 10.2 as The first three lines tell Travis CI to use Xcode 10.2