Renamed `then` to `thenDo` (due RxJS 2.3.12 changes).
Merge branch 'master' of https://github.com/Igorbek/rx.d.ts into RxJS
Merge pull request #2931 from Igorbek/RxJS

RxJS: renamed `then` to `thenDo` (due RxJS 2.3.12 changes)