message: build: update CMake to version 3.12.
diff: @@ -5,15 +5,19 @@ set -e
  # Setup basic requirements and install them.
  apt-get update
  export DEBIAN_FRONTEND=noninteractive
  -apt-get install -y wget software-properties-common make cmake git python python-pip \
  +apt-get install -y curl wget software-properties-common make git python python-pip \
  bc libtool ninja-build automake zip time golang g++ gdb strace wireshark tshark tcpdump
  +# Install cmake 3.12.
  +curl -sLO https://cmake.org/files/v3.12/cmake-3.12.3-Linux-x86_64.tar.gz
  +echo "0210f500c71af0ee7e8c42da76954298144d5f72f725ea381ae5db7b766b000e cmake-3.12.3-Linux-x86_64.tar.gz" | sha256sum --check
  +tar -zxf cmake-3.12.3-Linux-x86_64.tar.gz -C /usr --strip-components=1
  # clang 7.
  -wget -O - http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
  +curl http://apt.llvm.org/llvm-snapshot.gpg.key | apt-key add -
  apt-add-repository "deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-7 main"
  apt-get update
  apt-get install -y clang-7 clang-format-7 clang-tidy-7 lld-7
  # Bazel and related dependencies.
  -apt-get install -y openjdk-8-jdk curl
  +apt-get install -y openjdk-8-jdk
  echo "deb [arch=amd64] http://storage.googleapis.com/bazel-apt stable jdk1.8" | tee /etc/apt/sources.list.d/bazel.list
  curl https://bazel.build/bazel-release.pub.gpg | apt-key add -
  apt-get update
  