fix(nushell): Use correct env var for shims dir

asdf.nu

@@ -15,7 +15,7 @@ def --env configure-asdf [] {
       if ( $env | get --ignore-errors ASDF_DATA_DIR | is-empty ) {
         $env.HOME | path join '.asdf'
       } else {
-        $env.ASDF_DIR
+        $env.ASDF_DATA_DIR
       } | path join 'shims'
     )
     let asdf_bin_dir = ( $env.ASDF_DIR | path join 'bin' )