Fix crashing on git commit with no shrinkwrap updates in some cases

[sanderploegsma]

This fixes a crash when a package.json has devDependencies that are not sorted alphabetically. npm install --save-dev sorts dependencies in the package.json, so when a lockfile is not changed by this script, it tries to commit nothing, which fails.

Note: this only affects versions of npm where devDependencies are not shrinkwrapped, such as npm 3.

Example case: the package.json has the following devDependencies:

{
  "devDependencies": {
    "typescript": "^2.4.2",
    "jest": "^21.0.1",
    "ts-jest": "^20.0.0"
  }
}

Let's say ts-jest gets updated to 21.0.0. Greenkeeper would create a new commit where just the version in the package.json is updated and the greenkeeper-lockfile-update script is triggered. This:

• Reverts the greenkeeper commit using git revert -n HEAD
• Unstages the package.json using git reset HEAD
• Updates the shrinkwrap using npm install --save-dev ts-jest@21.0.0

Now, the following happens:

• git status --porcelain contains M package.json due to the sorting mentioned above, so the script does not return
• git add npm-shrinkwrap.json, git add package-lock.json and git add yarn.lock.json results in no staged changes
• git commit exits with non-zero.

[janl]

@boennemann could you have a look here. LGTM, but not too experienced with npm subtleties here. Mainly concerned with: does this break anything else?

[janl]

I’m closing this as we are getting ready to retire 1.x. Please re-open/rebase if this is still relevant in master