travis: fix a typo with TRAVIS_CPU_ARCH
travis: fix a typo with TRAVIS_CPU_ARCH

Travis CI uses "amd64" instead of "x86_64", fix the configuration.
* https://docs.travis-ci.com/user/environment-variables

Signed-off-by: Paul Moore <a027184a55211cd23e3f3094f1fdc728df5e0500@paul-moore.com>

seccomp/libseccomp,seccomp/libseccomp,seccomp/libseccomp