update hydrator with the new available interface/method in doctrine/common

There is a new interface in https://github.com/doctrine/common/pull/343, this is the implementation that will make possible to work with embeddables in DoctrineObject hydrator through this classmetadata implementation https://github.com/doctrine/doctrine2/pull/1185.

This modification in composer.json is purposeful and will be removed as soon as/if doctrine/common PR gets merged w/ forced push. The objective is to make it possible to travis test the DoctrineModule with the new interface and show that there are 3 PR's linked.
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