[Ada] Fix typo in comment for functional sets

[Pierre-Marie de Rodat via Gcc-patches]

Minor fix in a recently added comment.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

        * libgnat/a-cofuse.ads (Empty_Set): Fix typo in comment.
diff --git a/gcc/ada/libgnat/a-cofuse.ads b/gcc/ada/libgnat/a-cofuse.ads
--- a/gcc/ada/libgnat/a-cofuse.ads
+++ b/gcc/ada/libgnat/a-cofuse.ads
@@ -216,7 +216,7 @@ package Ada.Containers.Functional_Sets with SPARK_Mode is
          and Included_Except (Add'Result, Container, Item);
 
    function Empty_Set return Set with
-   --  Return an new empty set
+   --  Return a new empty set
 
      Global => null,
      Post   => Is_Empty (Empty_Set'Result);