add '/usr/bin/env bash' to the build templates

[qbit]

This makes lfetool use '/usr/bin/env bash' and also enables building on OpenBSD

[oubiwann]

First, I wanted to thank you for the contribution :-)

Second, we're going to be moving to lfetool-written-in-lfe, so I'm going to hold off on merging all but the most severe fixes.

Third, I'm not sure if I would survive a merge to master of a dependency on Perl (I might get lynched ...!) ;-)

[arpunk]

Hi @oubiwann,

This PR would also help using lfetool in FreeBSD due to bash being installed in /usr/local/bin. I agree on having Perl is a step backwards. Can't wait to try lfetool-written-in-lfe! :)

[oubiwann]

Ugh, didn't see this until now. It's got some conflicts that need to be resolved -- will take a look at it, if you can update ...