Remove Ubuntu 16.04 from CI
It's been deprecated, see
@@ -7,7 +7,7 @@ jobs:
unix-testing:
strategy:
matrix:
- os: [ubuntu-20.04, ubuntu-18.04, ubuntu-16.04, macos-10.15]
+ os: [ubuntu-20.04, ubuntu-18.04, macos-10.15]
cc: [gcc, clang]
buildsys: [make, cmake]
include:
