fix typo in ReadableStream section (#30)

Small typo fix in the ReadableStream section

Author: leonardfactory

README.md

@@ -157,7 +157,7 @@ There was some discussion to switch to ArrayBuffer in Issue https://github.com/s
 
 Blob is part of the W3C [File API](https://www.w3.org/TR/FileAPI/), not part of JavaScript, so it is not a viable solution to include in a TC39 Proposal. Furthermore, Blob typically includes a MIME Type but this proposal ignores the type. 
 
-### Why not ReableStream?
+### Why not ReadableStream?
 
 ReadableStream is part of the WHATWG [Streams](https://streams.spec.whatwg.org), not part of JavaScript, so it is not a viable solution to include in a TC39 Proposal. Furthermore, there is [no helper method](https://github.com/whatwg/streams/issues/1019) to turn a stream into a buffer so this won't solve the original motivation of writing isomorphic JavaScript.