Move connectionState/onConnectionStateChange to 2.18 in CHANGELOG

Change-Id: I272191c7b0adf1420d87f8264f6d2ef55b7b687d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/240482
Reviewed-by: Kevin Moore <kevmoo@google.com>
Commit-Queue: Srujan Gaddam <srujzs@google.com>

CHANGELOG.md

@@ -1,3 +1,12 @@
+## 2.18.0
+
+### Core libraries
+
+#### `dart:html`
+
+- Add `connectionState` attribute and `connectionstatechange` listener to
+  `RtcPeerConnection`.
+
 ## 2.17.0
 
 ### Core libraries
@@ -51,9 +60,6 @@
   return their correct return types now as well - `PerformanceEntry?` and
   `PerformanceMeasure?`, respectively.
 
-- Add `connectionState` attribute and `connectionstatechange` listener to
-  RTCPeerConnection.
-
 #### `dart:indexed_db`
 
 - `IdbFactory.supportsDatabaseNames` has been deprecated. It will always return