Bash not found on some distros

[aerique]

Both build.sh and gen-version use #!/bin/bash instead of #!/usr/bin/env bash which means Bash will not always be found (even on some Linux distributions!).

• https://github.com/PowerDNS/pdns-builder/blob/master/build.sh#L1
• https://github.com/PowerDNS/pdns-builder/blob/master/gen-version#L1

[aerique]

I'm just not sure on any disadvantages of using #!/usr/bin/env bash hence I'm not shooting in a PR right away.

edit: Konrad just replied with the reasons in chat:

That’s intentional. macOS ships a very old bash 3.2 as /bin/bash (last one that’s GPLv2) and I have a newer one in my path. I wanted to make sure that we do not use newer features.