Docs: gitDiffPathArguments ignoring `pubspec.lock `

[gmpassos]

Thx for the new option gitDiffPathArguments .

Please add to the documentation how to ignore the pubspec.lock, since it's not a trivial parameter for git users.

void main() {
  test('ensure_build',
      () => expectBuildClean(gitDiffPathArguments: [':!pubspec.lock']));
}

Best regards.