travis: fix macOS builds, avoid brew autoupdate
travis: fix macOS builds, avoid brew autoupdate

iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,LLNL/spack,LLNL/spack,LLNL/spack,iulian787/spack