Update docs/advanced/extensions.md

Author: tomchristie

docs/advanced/extensions.md

@@ -152,7 +152,7 @@ When using HTTP/2 there is no further response versioning included in the protoc
 
 The reason-phrase of the HTTP response, as bytes. For example `b"OK"`. Some servers may include a custom reason phrase, although this is not recommended.
 
-HTTP/2 Edwards does not include a reason phrase on the wire.
+HTTP/2 onwards does not include a reason phrase on the wire.
 
 When no key is included, a default based on the status code may be used.