Correct a typo in build-cache.md
Correct a typo in build-cache.md

Typo read 7xip instead of 7zip
gep13/website-1,gep13/website-1,appveyor/website,howitzer-industries/website,gep13/website-1,howitzer-industries/website,appveyor/website,howitzer-industries/website,appveyor/website