.travis.yml: Run 'make test' in Travis
.travis.yml: Run 'make test' in Travis

To catch things like gofmt errors [1] in CI testing (vs. leaving that
to manual review).

Also remove the vet and lint calls from .travis.yml, since those are
covered by the 'make test' invocation.

[1]: https://github.com/opencontainers/runtime-tools/pull/400#discussion_r123550759

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

opencontainers/runtime-tools,opencontainers/ocitools,liangchenye/ocitools,opencontainers/runtime-tools,wking/ocitools-v2,opencontainers/ocitools,wking/ocitools-v2,liangchenye/ocitools