Revert "Disable erroring TravisCI build"

[bhess]

This reverts commit b59d78c.

Travis build issue has been resolved, re-enabling the build.

To resolve: CROSS KATs on s390x fail, endianness issues?

• Does this PR change the input/output behaviour of a cryptographic algorithm (i.e., does it change known answer test values)? (If so, a version bump will be required from x.y.z to x.(y+1).0.)
• Does this PR change the list of algorithms available -- either adding, removing, or renaming? Does this PR otherwise change an API? (If so, PRs in fully supported downstream projects dependent on these, i.e., oqs-provider will also need to be ready for review and merge by the time this is merged.)