typo in saas_application_groups fetcher

[hellt]

https://github.com/nuagenetworks/vspk-python/blob/master/vspk/v5_0/nuenterprise.py#L414

[pdellaert]

We should have caught this before it went out, changing this now is going to break some stuff... i fear we are going to be stuck with this until i find a way to have both co-exist. (old code and new code)