1) For me it makes more sense to return latest registered implementation of a service
2) Actually this is consistent with the way ModernDependencyResolver works (https://github.com/reactiveui/ReactiveUI/blob/42e580f9d10db4e32c827273e57d0ac997421d86/ReactiveUI/ModernDependencyResolver.cs#L49)
Merge pull request #389 from journeyman/func-ioc-get-service-fix

Fix for GetService() implementation of FuncDependencyResolver