Some versions of Ubuntu have a very old clang-format. You can install a newer one (version 6.0) following these instructions.
For Ubuntu 16.04 (Xenial) add this to /etc/apt/sources.list:
deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-6.0 main
For other versions check apt.llvm.org.
In a terminal, execute these commands:
$ # Add the GPG key for the repository.
$ wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
$ # Install clang-format
$ apt-get update
$ apt-get install clang-format-6.0
$ # Make /usr/bin/clang-format point to the newly installed one.
$ update-alternatives --install /usr/bin/clang-format clang-format /usr/bin/clang-format-6.0 100