Fix missing addons line
@@ -33,6 +33,7 @@ matrix:
# Check that clang-format doesn't detect some files are not formatted.
- name: "Formatting check"
compiler: clang
+ addons:
apt:
sources:
- sourceline: 'deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main'
