Travis has the correct clang-tidy version of 7, while CircleCI needs clang-tidy-7.
Unnecessary line from Bionic 18.04 was removed. A proper version guard was included for clang. Xenial currently ships 3.8.
clang-tidy is currently set up with errors for all checks that do not warn. This is to prevent regressing the repo. Gradually these warnings should be removed in order to prevent further regresssions in warnings that do not have many occurences.
Vasily
Kung-vr