Upgrade peerDependency for rxjs 5

[mxdubois]

Hey,

Thanks for publishing this lib!

I'm using rxjs 5, which uses a different package name for some reason, so I needed to update the peerDependency.

This is a breaking change, of course, but I'll leave it to you to bump the version number as you're publishing.

Let me know if you need me to do anything else!

[staltz]

@mxdubois I'll wait until RxJS v5 is stable.