Fix a link.

Ix.NET/Source/System.Linq.Async/System/Linq/Operators/Concat.cs

@@ -159,8 +159,12 @@ namespace System.Linq
                             _current = _enumerator.Current;
                             return true;
                         }
-                        // note, this is simply to match the logic of 
-                        // https://github.com/dotnet/corefx/blob/ec2685715b01d12f16b08d0dfa326649b12db8ec/src/system.linq/src/system/linq/concatenate.cs#L173-L173
+
+                        //
+                        // NB: This is simply to match the logic of 
+                        //     https://github.com/dotnet/corefx/blob/f7539b726c4bc2385b7f49e5751c1cff2f2c7368/src/System.Linq/src/System/Linq/Concat.cs#L240
+                        //
+
                         var next = GetAsyncEnumerable(_counter++ - 1);
                         if (next != null)
                         {