certbund_contact use postgresql v>=9.5 features

[bernhardreiter]

Since a few month the minimal supported version of GNU is Ubuntu 16.04 LTS which comes with
https://packages.ubuntu.com/xenial/postgresql 9.5.

https://packages.debian.org/stretch/postgresql also comes with 9.6

So we can assume v>=9.5 as a minimum postgresql requirement and use the additional features.

E.g. see https://github.com/Intevation/intelmq/blob/ff5e42fc86abbd40d77d7c7561c80584468a13a4/intelmq/bots/experts/certbund_contact/initdb.sql#L174