.travis.yml: fixup install
.travis.yml: fixup install

* Use trusty (14.04 LTS) release of ubuntu to prevent package update
  issues

* install packages non-interactive

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,jluebbe/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,ejoerns/rauc,jluebbe/rauc,rauc/rauc