composer.lock shall be removed from .gitignore

[chrodriguez]

Hello, I've followed the instructions for installing sylius standard in development mode. It suggests to clone this repo (or creating your own based on this template).

When you are working with docker, the lifecycle will not consider creating a project using composer, like:

 php composer.phar create-project sylius/sylius-standard project

Instead,the first command a developer would run is (considering some ad-hoc modifications considering developers operating system to docker-compose):

docker-compose up

Without composer workflow, post-create-project-cmd will never be called, and composer.lock will be always ignored. Issue #665 and PR 855 fixes this problem when working with composer, but I think removing line 19 of .gitignore would be a better approach.

I would like to create a PR, but first I would like to know If there is any reason to keep this file ignored in this repo as it is not a composer library, and composer itself recommends to version composer.lock file.

Thanks in advance