[publish] Faire une vérification du format du slug avant la publication

<a href="https://github.com/kosssi"><img src="https://avatars2.githubusercontent.com/u/1135513?v=4" align="left" width="96" height="96" hspace="10"></img></a> **Issue by [kosssi](https://github.com/kosssi)**
_Tuesday Mar 27, 2018 at 09:35 GMT_
_Originally opened as https://github.com/cozy/cozy-app-publish/issues/2_

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