Increase Travis cache size [ci skip]
Increase Travis cache size [ci skip]

With compression disabled, the cache is too small for builds that
use debug info, and causes 100% miss rate.

webmaster128/botan,randombit/botan,webmaster128/botan,webmaster128/botan,webmaster128/botan,randombit/botan,randombit/botan,webmaster128/botan,randombit/botan,randombit/botan