Can install with Symfony 2.4

Fixes https://github.com/KnpLabs/KnpTimeBundle/issues/49
Revert https://github.com/KnpLabs/KnpTimeBundle/commit/d2b0f7fc64e7128e6d8c0693d0b548045eec6db5

Revert commit: https://github.com/KnpLabs/KnpTimeBundle/commit/d2b0f7fc64e7128e6d8c0693d0b548045eec6db5
Merge pull request #50 from thvd/patch-1

Can install with Symfony 2.4