Carthage fails to build

I am seeing the following when trying to build with latest Carthage and 4.0 of RxViewModel:


```
Carthage/Checkouts/RxViewModel/Source/RxViewModel.swift:13:8: error: no such module 'RxSwift'
import RxSwift
       ^

** BUILD FAILED **

Cartfile.resolved

github "ReactiveX/RxSwift" "3.5.0"
github "RxSwiftCommunity/RxViewModel" "4.0.0"

```