make up.nu much simpler (#391)

Now nu supports String multiplications!

filesystem/up.nu

@@ -1,15 +1,6 @@
-def up_inner [limit: int] {
-  mut x = []
-  for $e in 0..$limit { $x = $x ++ "." }
-  $x | str collect
-}
-
 # Go up a number of directories
 def-env up [
     limit = 1: int # The number of directories to go up (default is 1)
   ] {
-    cd (
-    (up_inner $limit)
-    | into string
-    )
+    cd ("." * ($limit + 1))
 }