make shebangs portable

[NANASHI0X74]

change the shebangs for the scripts that generate samples to locate bash via /usr/bin/env
Some systems, like nixOS, don't use the linux filesystem hierarchy standard and/or have a bash binary in that path. /usr/bin/env is available on most systems even that don't go with the regular FHS and will locate the interpreter using the user's $PATH instead. for more info: https://unix.stackexchange.com/questions/29608/why-is-it-better-to-use-usr-bin-env-name-instead-of-path-to-name-as-my

[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[NANASHI0X74]

oh yeah thanks for pointing that out... I guess I'll have to fix the email address. But for this commit I don't really care :p you can still merge it regardless