minor #855 [Composer] Remove composer.lock from .gitignore after crea…

…ting the project (artyuum)

This PR was merged into the 1.12 branch.

Discussion
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This fixes the issue #665.

Inspired by [sulu/skeleton](https://github.com/sulu/skeleton/blob/9f6f4d5792a737e96e20b5d9cce9523e43e064b7/composer.json#L118).

Can you review this, please? @lchrusciel 

Commits
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526d8e5 Add post create project command to remove composer.lock from .gitignore
a4e6505 Prevent blank line after removing composer.lock in .gitignore

composer.json

@@ -109,6 +109,7 @@
             "@auto-scripts"
         ],
         "post-create-project-cmd": [
+            "@php -r \"file_put_contents('.gitignore', str_replace('/composer.lock' . PHP_EOL, '', file_get_contents('.gitignore')));\"",
             "@php bin/console sylius:inform-about-gus --ansi",
             "@php bin/console sylius:show-available-plugins --ansi"
         ],