[release] package.json: v0.28.1

Update version string for release

Change-Id: I06bdbd26e6623bfb22a062264b7f3d1d90e6ca47
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/352053
Trust: Hyang-Ah Hana Kim <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
TryBot-Result: kokoro <[email protected]>
Reviewed-by: Suzy Mueller <[email protected]>

Author: hyangah

package-lock.json

@@ -1,7 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.28.0",
+  "version": "0.28.1",
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",
   "author": {