CHANGELOG.md: Update changelog for release continued

Change-Id: Ib85c505426ce87d42a9c0bc44304c16f720618fb
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/380814
Trust: Suzy Mueller <[email protected]>
Run-TryBot: Suzy Mueller <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Hyang-Ah Hana Kim <[email protected]>
(cherry picked from commit b5b4835)
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/380815

Author: suzmue

CHANGELOG.md

@@ -1,4 +1,6 @@
-## v0.31.0 - 20 Jan, 2022
+## v0.31.0 - 26 Jan, 2022
+
+A list of all issues and changes can be found in the [v0.31.0 milestone](https://github.com/golang/vscode-go/milestone/41) and [commit history](https://github.com/golang/vscode-go/compare/v0.30.0...v0.31.0).
 
 ### Fixes