Update deprecated code examples in UnitTests.md (#1766)
Update deprecated code examples in UnitTests.md (#1766)

The `next()` global function is planned for future deprecation. Now using `Recorded.next()` instead.
ReactiveX/RxSwift,kzaher/RxSwift,kzaher/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift