Fixed missing travis dependency for Ubuntu trusty
Fixed missing travis dependency for Ubuntu trusty

gstreamer1.0-plugins-base was removed in the updated 2017Q2 trusty image (https://github.com/travis-ci/build-environment-updates/blob/master/2017Q2/gce/garnet-trusty/dpkg-manifest.diff) and gir1.2-gst-plugins-base-1.0 does not depend on gstreamer1.0-plugins-base in trusty (fixed in xenial).
kingosticks/mopidy-spotify,mopidy/mopidy-spotify