[CI] Downgrade to 14.04 Trusty.
[CI] Downgrade to 14.04 Trusty.

> If you’re using macOS or Trusty environments, you can also use Rubinius.
@see https://docs.travis-ci.com/user/languages/ruby/#rubinius

adhearsion/ruby_speech,adhearsion/ruby_speech,adhearsion/ruby_speech