chore(package.json): bump rxjs to rc4, remove chai types

[jayphelps]

rc4 fixed the ReactiveX/rxjs#2112 so the chai types are no longer needed.

rc4 had other very minor changes: https://github.com/ReactiveX/rxjs/blob/master/CHANGELOG.md#500-rc4-2016-11-19

Bug Fixes

• partition: handles thisArg as expected (#2138) (6cf7296)
• timeout: throw traceable TimeoutError (#2132) (9ebc46b)

[tobymurray]

Whoops! Didn't mean to drag you into this personal project @jayphelps - didn't realize GitHub picked up the issue references from commits. Just wanted to leave myself a note to pick up the fix when it was available. Thanks so much for taking the time, I appreciate it!

[jayphelps]

you certainly didn't drag me in. As a courtesy I was following up with every project I could find that had to work around the issue 🎉 I was snooping :o)