[Feature:Travis] Use Ubuntu Bionic for Travis-CI builds (#5472)
[Feature:Travis] Use Ubuntu Bionic for Travis-CI builds (#5472)

Signed-off-by: Matthew Peveler <ceb7192332cc0210660ce4c985cae5ba0e431884@gmail.com>
Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,RCOS-Grading-Server/HWserver,Submitty/Submitty,RCOS-Grading-Server/HWserver,Submitty/Submitty,Submitty/Submitty