"The call is ambiguous between the following methods" for services.AddCors()

I am using Visual Studio Community 2015 Update 3. I am busy attempting to enable CORS as per this resource: https://docs.asp.net/en/latest/security/cors.html

• I created a new .NET Core Web API project.
• In Startup.cs, under ConfigureServices() I added: services.AddCors()
• However, after adding the following dependency to project.json: "Microsoft.AspNet.Cors": "6.0.0-rc1-final", I got the following error: The call is ambiguous between the following methods or properties: 'Microsoft.Extensions.DependencyInjection.CorsServiceCollectionExtensions.AddCors(Microsoft.Extensions.DependencyInjection.IServiceCollection)' and 'Microsoft.Extensions.DependencyInjection.CorsServiceCollectionExtensions.AddCors(Microsoft.Extensions.DependencyInjection.IServiceCollection)'

I can confirm that removing that dependency resolves the error. Any guidance would be greatly appreciated.