Revision 088b116a0e27faa0e1a7384dd4f3f6a9d5a8a3b6

minor #340 Updated composer.json to include new security check version (Lucas Matte)

This PR was squashed before being merged into the 5.0.x-dev branch (closes #340).

Discussion
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Updated composer.json to include new security check version

This pull requests updates `composer.json` to allow for version 5 of the security checker to be used in a project. This is needed since the old `https://security.sensiolabs.org/check_lock` is going to be retired. The 5.0 version moved the url to `https://security.symfony.com/check_lock`.

Commits
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2f2d0d9 Updated composer.json to include new security check version