Doesn't work well with environments with non posix compliant shell set as default

[2gn]

Steps to reproduce

1. install mimi
2. chsh -s /usr/bin/nu (or wherever nushell is installed)
3. run xdg-open <url> for example

~> xdg-open https://github.com
'chromium' https://github.com
Error: nu::parser::parse_mismatch

  × Parse mismatch during operation.
   ╭─[source:1:12]
 1 │ 'chromium' https://github.com
   ·            ─────────┬────────
   ·                     ╰── expected operator
   ╰────

This happens even if running mimi from outside nushell, like from zsh. It is probably because mimi depends on default user shell to execute the last step.