Release 2.0.0-RC4

1.2.1 - Update changes.md

Update changes.md for RC3

1.2.0 changes.md

Update changes.md and readme.md

Update changes.md

Update changes.md and readme.md

Release 1.1.9 update changes.md (ReactiveX#4345)

Update changes.md

Release 1.1.7 changes.md update (ReactiveX#4184)

* Release 1.1.7 changes.md update

* Mention last 2 PRs merged