bin/dev.sh does not correctly detect shell on all distros

bin/dev.sh uses hardcoded paths to /bin/bash and /bin/zsh. However depending on the distro used, these binaries can be stored elsewhere.

For example, in my debian system, zsh is stored in /usr/bin/zsh.

This detection should be made more robust (e.g. using globs)

(MR incoming on this issue 😉)