Update to Xenial base and install pinned Go dependencies (fixing #278).
Update to Xenial base and install pinned Go dependencies (fixing #278).

theurere/spreed-webrtc,theurere/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc,strukturag/spreed-webrtc,strukturag/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc,theurere/spreed-webrtc,strukturag/spreed-webrtc