Reacting to DI changes

src/Microsoft.Framework.WebEncoders/EncoderServiceCollectionExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using Microsoft.Framework.DependencyInjection.Extensions;
 using Microsoft.Framework.Internal;
 using Microsoft.Framework.OptionsModel;
 using Microsoft.Framework.WebEncoders;