Respect current shell

[andor44]

It'd be nice if this plugin respected the currently running shell instead of launching bash unconditionally. I use zsh personally, and that's what all my autocompletion, etc. are configured for. You could simply check if $SHELL is set, and if so use that, otherwise fall back to bash. This would also solve problems like #6 without needing to install bash into Alpine based images, for example.

[rimusz]

here we go #13