[fixed] typo in README

README.md

@@ -7,7 +7,7 @@
 
 There are a lot of great Observable implementations, but they're baked into featureful libraries which contribute to both complexity and filesize.  We wanted the simplest-possible Observable implementation, with no operators, no fancy scheduling: [read the entire source](https://github.com/material-motion/indefinite-observable-js/blob/develop/src/IndefiniteObservable.ts) without scrolling.
 
-Indefinite Observable is a subset of the [TC39 Observable proposal](https://tc39.github.io/proposal-observable/) that never `complete`s or `error`s.  It implements the [minimal-necessary functionality](https://en.wikipedia.org/wiki/You_aren't_gonna_need_it), but it should be completely interchangable with the TC39 proposal for the subset that it does implement.
+Indefinite Observable is a subset of the [TC39 Observable proposal](https://tc39.github.io/proposal-observable/) that never `complete`s or `error`s.  It implements the [minimal-necessary functionality](https://en.wikipedia.org/wiki/You_aren't_gonna_need_it), but it should be completely interchangeable with the TC39 proposal for the subset that it does implement.
 
 If you want a complete Observables library that works out-of-the-box, check out [xstream](https://github.com/staltz/xstream/), [RxJS](https://github.com/ReactiveX/RxJS/), [Most](https://github.com/cujojs/most/), [Bacon](https://github.com/baconjs/bacon.js/), or [Kefir](https://github.com/rpominov/kefir/).  If you want to build your own Observables library that includes just the functionality you need, try [Indefinite Observable](https://github.com/material-motion/indefinite-observable-js/#indefinite-observable).