Travis: Enable zstd
When we make chutney work on Bionic or Xenial (legacy/trac#32240 (moved)), we can enable zstd on Travis.
We could have a different package list for Bionic and Trusty, but that kind of duplication is error-prone.
When we make chutney work on Bionic or Xenial (legacy/trac#32240 (moved)), we can enable zstd on Travis.
We could have a different package list for Bionic and Trusty, but that kind of duplication is error-prone.