Updated rx.d.ts and rx-lite.d.ts to version 2.2.20
Updated rx.aggregates.d.ts t oversion 2.2.20
Updated rx.async.d.ts to version 2.2.20
Updated RxJS-BackPressure to v2.2.20
Updated RxJS-Experimental to v2.2.20
Version bump to 2.2.20 for all other files
Merge pull request #2036 from Igorbek/master

RxJS: updated to version 2.2.20