Adds `validate-podspec.sh` to `pre-release-tests.sh`(Release mode).
Adds `validate-podspec.sh` to `pre-release-tests.sh`(Release mode).

thanegill/RxSwift,kzaher/RxSwift,thanegill/RxSwift,cfraz89/RxSwift,ReactiveX/RxSwift,shiratsu/RxSwift,tottakai/RxSwift,thanegill/RxSwift,hsoi/RxSwift,kzaher/RxSwift,cfraz89/RxSwift,tottakai/RxSwift,KyoheiG3/RxSwift,tottakai/RxSwift,hsoi/RxSwift,ReactiveX/RxSwift,hsoi/RxSwift,ReactiveX/RxSwift,hsoi/RxSwift,thanegill/RxSwift,shiratsu/RxSwift,cfraz89/RxSwift,kzaher/RxSwift,KyoheiG3/RxSwift,KyoheiG3/RxSwift,kzaher/RxSwift,shiratsu/RxSwift,cfraz89/RxSwift