Update composer.json

Bump doctrine common dependency for symfony 2.1 users
merged branch guilhermeblanco/patch-13 (PR #7160)

This PR was merged into the 2.1 branch.

Commits
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f0704aa Update composer.json

Discussion
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Update composer.json

Bump doctrine common dependency for symfony 2.1 users

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by stof at 2013-02-22T17:32:25Z

@guilhermeblanco what about using ``~2.2`` as Doctrine keeps BC between minor versions ?