Export `AbortError` (Fixes: #792)

Signed-off-by: Richie Bendall <richiebendall@gmail.com>

docs/CHANGELOG.md

@@ -3,6 +3,12 @@ Changelog
 
 # 3.x release
 
+## v3.0.0-beta.6
+
+**Work in progress!**
+
+- Fix: Export the `AbortError` class.
+
 ## v3.0.0-beta.5
 
 > NOTE: Since the previous beta version included serious issues, such as [#749](https://github.com/node-fetch/node-fetch/issues/749), they will now be deprecated. 

src/index.js

@@ -309,3 +309,4 @@ fetch.Headers = Headers;
 fetch.Request = Request;
 fetch.Response = Response;
 fetch.FetchError = FetchError;
+fetch.AbortError = AbortError;