Make sure RxKotlin operators are up-to-date

[DavidMGross]

Some new ones may have come in via 0.30.1 for instance

https://github.com/ReactiveX/RxKotlin/releases/tag/v0.30.1

[DavidMGross]

See also:

• combineLatest and zip extensions for observable lists RxKotlin#32
• plusAssign operator for CompositeSubscription RxKotlin#33

[DavidMGross]

See also ReactiveX/RxKotlin#59 (Single)

[DavidMGross]

See also ReactiveX/RxKotlin#58 (removal of some operators)