zendframework/zf2 — pull request #6618 by BreyndotEchse (2014-09-01 08:31:18+00:00)
Title: Do not gitignore composer.lock

https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file
"Commit your application's composer.lock (along with composer.json) into version control.

This is important because the install command checks if a lock file is present, and if it is, it downloads the versions specified there (regardless of what composer.json says)."