Require dev doctrine/mongodb-odm

Sometimes it is useful to run all specs with a simple command.

Running specs before:

```
$ ./bin/phpspec run
Sylius/Bundle/ResourceBundle/Doctrine/ODM/MongoDB/DocumentRepository
  43  ! it is initializable
      exception [exc:ReflectionException("Class Doctrine\ODM\MongoDB\DocumentManager does not exist")] has been thrown.

Sylius/Bundle/ResourceBundle/Doctrine/ODM/MongoDB/DocumentRepository
  48  ! it implements Sylius repository interface
      exception [exc:ReflectionException("Class Doctrine\ODM\MongoDB\DocumentManager does not exist")] has been thrown.

Sylius/Bundle/ResourceBundle/Doctrine/ODM/MongoDB/DocumentRepository
  53  ! it creates Pagerfanta paginator
      exception [exc:ReflectionException("Class Doctrine\ODM\MongoDB\DocumentManager does not exist")] has been thrown.

                       100%                        1700
264 specs
1700 examples (1697 passed, 3 broken)
12487ms
```

And after my changes:

```
$ ./bin/phpspec run
                       100%                        1700
264 specs
1700 examples (1700 passed)
12911ms
```