Lock down build image to Ubuntu Precise for the time being.
Lock down build image to Ubuntu Precise for the time being.

For details, see:

  https://blog.travis-ci.com/2017-07-11-trusty-as-default-linux-is-coming

Signed-off-by: Krzysztof Wilczynski <5f1c0be89013f8fde969a8dcb2fa1d522e94ee00@linux.com>

kwilczynski/ruby-magic,kwilczynski/ruby-magic