fix: nushell spread operator

[deas]

Summary

With nushell 0.94.2 I get the following error:

$ asdf plugin list
Error: nu::shell::cannot_pass_list_to_external

  × Lists are not automatically spread when calling external commands
     ╭─[/home/deas/.asdf/asdf.nu:110:27]
 109 │ 
 110 │         ^asdf plugin list $flags | lines | parse -r $template | str trim
     ·                           ───┬──
     ·                              ╰── Spread operator (...) is necessary to spread lists
 111 │     }
     ╰────
  help: Either convert the list to a string or use the spread operator, like so: ...$flags

This change fixes that for me.