Invalid data provider in the `ObjectManagerDecoratorTest`

[Ocramius]

As per #765 (comment) by @Majkl578, the test suite currently loads an invalid data provider:

1) Warning
The data provider specified for Doctrine\Tests\Common\Persistence\ObjectManagerDecoratorTest::testAllMethodCallsAreDelegatedToTheWrappedInstance is invalid.

See Travis: https://travis-ci.org/doctrine/common/jobs/197349731#L228

[Majkl578]

Caused by 6a56df9.

Ping @ondrejmirtes.

[ondrejmirtes]

Fixed in #773.