message: Attempt to fix broken npm version on node v5 and v4
diff: language: node_js
  -node_js:
  - - "9"
  - - "8"
  - - "7"
  - - "6"
  - - "5"
  - - "4"
  +matrix:
  + include:
  + - node_js: "9"
  + env: NPM_VERSION=""
  + - node_js: "9"
  + env: NPM_VERSION=""
  + - node_js: "7"
  + env: NPM_VERSION=""
  + - node_js: "6"
  + env: NPM_VERSION=""
  + - node_js: "5"
  + env: NPM_VERSION="@5"
  + - node_js: "4"
  + env: NPM_VERSION="@5"
  # Allow Travis tests to run in containers.
  sudo: false
  # Update package-lock.json after test runs:
  before_install:
  - - npm install -g npm
  + - npm install -g npm$NPM_VERSION
  - npm install -g greenkeeper-lockfile@1
  before_script: greenkeeper-lockfile-update
  after_script: greenkeeper-lockfile-upload
  