Fix response cookies namespace.

src/Microsoft.AspNet.PipelineCore/Collections/ResponseCookiesCollection.cs

@@ -2,9 +2,10 @@
 using System.Collections.Generic;
 using System.Globalization;
 using System.Linq;
+using Microsoft.AspNet.Abstractions;
 using Microsoft.AspNet.Abstractions.Infrastructure;
 
-namespace Microsoft.AspNet.Abstractions.Collections
+namespace Microsoft.AspNet.PipelineCore.Collections
 {
     /// <summary>
     /// A wrapper for the response Set-Cookie header

src/Microsoft.AspNet.PipelineCore/DefaultCanHasResponseCookies.cs

@@ -1,5 +1,4 @@
 using Microsoft.AspNet.Abstractions;
-using Microsoft.AspNet.Abstractions.Collections;
 using Microsoft.AspNet.FeatureModel;
 using Microsoft.AspNet.HttpFeature;
 using Microsoft.AspNet.PipelineCore.Collections;