Use Existing Path Env Var for FNM (#632)

The module for `fnm` did not set the path for Windows correctly. I fixed
it by searching for the used `Path` variable (or `PATH`) and use that
instead.

Works now better on Windows without breaking other OSes.

modules/fnm/fnm.nu

@@ -1,20 +1,22 @@
 export-env {
     def fnm-env [] {
         mut env_vars = {}
-        let pwsh_vars = (^fnm env --shell power-shell)
+        let pwsh_vars = (
-        let var_table = ($pwsh_vars
+            ^fnm env --shell power-shell | 
-            | lines
+            lines | 
-            | parse "$env:{key} = \"{value}\""
+            parse "$env:{key} = \"{value}\""
         )
-        for v in $var_table  {
+
-            mut value: any = null
+        # fnm-prefixed vars
-            if ($v.key | str downcase) == 'path' {
+        for v in ($pwsh_vars | range 1..) { 
-                $value = ($v.value | split row (char esep))
+            $env_vars = ($env_vars | insert $v.key $v.value) 
-            } else {
-                $value = $v.value
-            }
-            $env_vars = ($env_vars | insert $v.key $value)
         }
+
+        # path
+        let env_used_path = ($env | columns | where {str downcase | $in == "path"} | get 0)
+        let path_value = ($pwsh_vars | get 0.value | split row (char esep))
+        $env_vars = ($env_vars | insert $env_used_path $path_value)
+
         return $env_vars
     }