Docs: Limit Microarch on Travis CI (#16200)
Docs: Limit Microarch on Travis CI (#16200)

Update the travis CI docs: limiting the microarch is essential
for caching.
LLNL/spack,LLNL/spack,iulian787/spack,iulian787/spack,LLNL/spack,iulian787/spack,iulian787/spack,iulian787/spack,LLNL/spack,LLNL/spack