Update validate-playgrounds.sh
Update validate-playgrounds.sh

I revised my previous change to get validate-playgrounds.sh to build
the RxPlaygrounds dynamic framework before attempting to build the
playgrounds test application.

ReactiveX/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift