error CS1061: 'IServiceCollection' does not contain a definition for'AddWebpack' and no extension method 'AddWebpack' accepting a first argument of type 'IServiceCollection' could be found (are you missing a using directive o assembly reference?)

{
     "version": "1.0.0-*",
       "dependencies": {
         "Microsoft.AspNetCore.Diagnostics": "1.0.0",
         "Microsoft.AspNetCore.Mvc": "1.0.1",
         "Microsoft.AspNetCore.Razor.Tools": {
              "version": "1.0.0-preview2-final",
              "type": "build"
               },
         "Microsoft.AspNet.SignalR.Client": "2.2.1",
         "Microsoft.AspNetCore.SignalR.Server": "0.1.0-rtm-21431",
         "Microsoft.AspNet.SignalR.SystemWeb": "2.2.1",
         "Microsoft.AspNet.SignalR.JS": "2.2.1",
         "Microsoft.AspNetCore.WebSockets.Server": "0.1.0-rc2-final",
         "System.Xml.XmlSerializer": "4.0.11",
         "React.AspNet": "3.0.0-rc1",
         "Microsoft.AspNetCore.Routing": "1.0.1",
         "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0",
         "Microsoft.AspNetCore.Server.Kestrel": "1.0.1",
         "Microsoft.AspNetCore.StaticFiles": "1.0.0",
         "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0",
         "Microsoft.Extensions.Configuration.Json": "1.0.0",
         "Microsoft.Extensions.Configuration.CommandLine": "1.0.0",
         "Microsoft.Extensions.Logging": "1.0.0",
         "Microsoft.Extensions.Logging.Console": "1.0.0",
         "Microsoft.Extensions.Logging.Debug": "1.0.0",
         "Microsoft.Extensions.Options.ConfigurationExtensions": "1.0.0",
         "Microsoft.VisualStudio.Web.BrowserLink.Loader": "14.0.0",
         "Microsoft.Owin.Host.SystemWeb": "3.0.1",
         "Microsoft.Owin": "3.0.1",
         "Microsoft.Owin.Security": "3.0.1",
         "Webpack": "3.0.0"
     },
      "tools": {
         //"BundlerMinifier.Core": "2.0.238",
         //"Microsoft.AspNetCore.Razor.Tools": "1.0.0-preview2-final",
         "Microsoft.AspNetCore.Server.IISIntegration.Tools": "1.0.0-preview2-final"
      },
      "frameworks": {
          "netcoreapp1.1": {
               "dependencies": {
                    "Microsoft.NETCore.App": {
                          "version": "1.1.0-preview1-001100-00",
                          "type": "platform"
                     }
                },
                "imports": [
                    "net451",
                    "dnxcore50"
                  ]
                 }
            },
       "buildOptions": {
          "emitEntryPoint": true,
          "preserveCompilationContext": true
       ,
      "runtimeOptions": {
           "configProperties": {
               "System.GC.Server": true
               }
            },
       "publishOptions": {
            "include": [
                "wwwroot",
                "**/*.cshtml",
                "appsettings.json",
                "web.config"
                ]
       },
      "scripts": {
      "precompile": [ "dotnet bundle" ],
      "prepublish": [ "bower install" ],
      "postpublish": [ "dotnet publish-iis --publish-folder %publish:OutputPath% --framework %publish:FullTargetFramework%" ]
},
      "tooling": {
      "defaultNamespace": "Rebellion"
     }
 }

public void ConfigureServices(IServiceCollection services)
{
     // Add framework services.
     services.AddMvc();
     services.AddSignalR();
     services.AddWebpack();
}