message: docs(changelog): fix mention of `stream` feature to `unstable-stream`
diff: * **body:**
  * identify aborted body write errors ([dc54ee19](https://github.com/hyperium/hyper/commit/dc54ee199f2d19d65913d224b900a61ab3bf2415))
  - * put `Stream` impl for `Body` behind `stream` feature ([511ea388](https://github.com/hyperium/hyper/commit/511ea3889b5cceccb3a42aa72465fe38adef71a4))
  + * put `Stream` impl for `Body` behind `unstable-stream` feature ([511ea388](https://github.com/hyperium/hyper/commit/511ea3889b5cceccb3a42aa72465fe38adef71a4))
  * **server:** introduce `Accept` trait ([b3e55062](https://github.com/hyperium/hyper/commit/b3e5506261c33dcaca39a126e891a0b9d5df5eea))
  @@ -2472,4 +2472,3 @@ tag is now in a tuple.
  * **headers:**
  * fix fmt_header outputs of several headers ([aa266653](https://github.com/hyperium/hyper/commit/aa26665367bde895ce02ad2a8e1a372f00719852), closes [#246](https://github.com/hyperium/hyper/issues/246))
  * don't use Show to write UserAgent header ([c8e334aa](https://github.com/hyperium/hyper/commit/c8e334aaebb5522a86d47f7e3c33836d2061cb65))
  -
  