update CHANGELOG

[skip ci]

Author: doghappy

CHANGELOG.md

@@ -5,6 +5,22 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [3.0.0] - 2021-9-13
+
+SocketIOClient v3.x supports http polling and websocket, socket.io server v2.x is no longer supported.
+
+### Added
+
+- http polling
+- SocketIOClient.ClientWebSocketProvider
+- If you want to use http polling and do not want the library to upgrade the transport, please set `Options.AutoUpgrade = false`.
+
+### Removed
+
+- EIO option
+- SocketIOClient.Socket
+- socket.io server v2.x is no longer supported. If a large number of users use this version, please feedback.
+
 ## [2.3.1] - 2021-8-3
 
 ### Changed