.travis.yml: Remove sandbox/target from cache
.travis.yml: Remove sandbox/target from cache

alekseysidorov/exonum,exonum/exonum,alekseysidorov/exonum,exonum/exonum,alekseysidorov/exonum,exonum/exonum,exonum/exonum,alekseysidorov/exonum