Problem parsing package version with new Flex release

To reproduce:

```
symfony new flex_orm_pack
cd flex_orm_pack
composer require doctrine/annotations form validator twig-bundle orm-pack security
```

Error:

> Could not parse version constraint "orm-pack".

Error noticed in MakerBundle test suite :). The errors seems to have shown up recently, so I'm guessing it's related to the most recent version.

Thanks!