message: ci: Upgrade images to version 13
  This upgrades CMake from 3.13 to 3.15
diff: version: 2.1
  executors:
  + lint:
  + docker:
  + - image: ethereum/cpp-build-env:13-lint
  linux-gcc-9:
  docker:
  - - image: ethereum/cpp-build-env:12-gcc-9
  + - image: ethereum/cpp-build-env:13-gcc-9
  linux-clang-9:
  docker:
  - - image: ethereum/cpp-build-env:12-clang-9
  + - image: ethereum/cpp-build-env:13-clang-9
  macos:
  macos:
  xcode: 11.3.0
  @@ -58,8 +61,7 @@ commands:
  jobs:
  lint:
  - docker:
  - - image: ethereum/cpp-build-env:12-lint
  + executor: lint
  steps:
  - checkout
  - run:
  @@ -98,12 +100,6 @@ jobs:
  BUILD_TYPE: Coverage
  TESTS_FILTER: unittests
  steps:
  - - run:
  - name: "Install lcov"
  - working_directory: /tmp
  - command: |
  - curl -sL http://downloads.sourceforge.net/ltp/lcov-1.14.tar.gz | tar xz --strip=1
  - sudo make install
  - build
  - test
  - run:
  