Fix build error

src/DotNetCore.CAP/CAP.Builder.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Core Community. All rights reserved.
 // Licensed under the MIT License. See License.txt in the project root for license information.
 
+using DotNetCore.CAP.Filter;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.DependencyInjection.Extensions;