Improving source copy comment in Set.

Ix.NET/Source/System.Linq.Async/System/Linq/Set.cs

@@ -2,11 +2,12 @@
 // The .NET Foundation licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information. 
 
+// Copied from https://github.com/dotnet/corefx/blob/ec2685715b01d12f16b08d0dfa326649b12db8ec/src/System.Linq/src/System/Linq/Set.cs
+
 using System.Collections.Generic;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 
-// from https://github.com/dotnet/corefx/blob/ec2685715b01d12f16b08d0dfa326649b12db8ec/src/System.Linq/src/System/Linq/Set.cs
 namespace System.Linq
 {
     [ExcludeFromCodeCoverage]