Use proper flag for xz files
Use proper flag for xz files

craigcitro/travis-build,jhass/travis-build,andyli/travis-build,andyli/travis-build,kevmoo/travis-build,JuliaCI/travis-build,akoeplinger/travis-build,akoeplinger/travis-build,JuliaCI/travis-build,kevmoo/travis-build,jhass/travis-build,craigcitro/travis-build