[Travis] Add Ubuntu 20.04, OSX XCode 11.5 jobs#2953

Merged

saihv merged 4 commits intomicrosoft:masterfrom rajat2004:travis-focal-osx

Oct 3, 2020

+23-7

Commits on Oct 2, 2020

Commits on Oct 3, 2020

Install catkin_tools from source for Ubuntu 20.04
rajat2004
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