fs.ensureFile to fix missing .tessel dir in Preferences.write
fs.ensureFile to fix missing .tessel dir in Preferences.write

Fix for issue #820
tikurahul/t2-cli,rwaldron/t2-cli,tikurahul/t2-cli,tikurahul/t2-cli,nodebotanist/t2-cli,rwaldron/t2-cli,tessel/t2-cli,rwaldron/t2-cli,nodebotanist/t2-cli,tessel/t2-cli,nodebotanist/t2-cli,tessel/t2-cli