:nail_care: Support TLS 1.2 by using Trusty distro
:nail_care: Support TLS 1.2 by using Trusty distro

Hashicorp have configured the webserver for
https://releases.hashicorp.com to only support TLS v1.2 and above.
Migrating the build environment to use Trusty as the distribution is
required in order to use OpenSSL libraries which support this version of
TLS.

See: https://github.com/travis-ci/travis-ci/issues/7131

hashicorp/vault-rails,hashicorp/vault-rails