Fix markdown url for [combinatorial explosion].
Fix markdown url for [combinatorial explosion].

Remove extra space that caused a glitch when parsing markdown.
kzaher/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,ReactiveX/RxSwift,ReactiveX/RxSwift,kzaher/RxSwift,kzaher/RxSwift