message: [CI] upgrade stretch to buster
  In CircleCI setup, bump rust:stretch to rust:buster for builders. This
  is to keep it consistent with Docker build.
  Closes:
  Approved by: bmwill
diff: @@ -3,11 +3,11 @@ version: 2.1
  executors:
  build-executor:
  docker:
  - - image: circleci/rust:stretch
  + - image: circleci/rust:buster
  resource_class: 2xlarge
  audit-executor:
  docker:
  - - image: circleci/rust:stretch
  + - image: circleci/rust:buster
  resource_class: xlarge
  terraform-executor:
  docker:
  @@ -44,9 +44,8 @@ commands:
  - run:
  name: Install Dependencies
  command: |
  - sudo sh -c 'echo "deb http://deb.debian.org/debian stretch-backports main" > /etc/apt/sources.list.d/backports.list'
  sudo apt-get update
  - sudo apt-get install -y protobuf-compiler/stretch-backports cmake curl
  + sudo apt-get install -y cmake curl
  sudo apt-get clean
  sudo rm -r /var/lib/apt/lists/*
  rustup component add clippy rustfmt
  