[release] package.json: update version info in package.json

It should be v0.18.1

https://github.com/golang/vscode-go/runs/1334020348?check_suite_focus=true

Change-Id: I651703cbef4057be984c09f721aacba5eb1a7c26
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/266757
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>

Author: hyangah

package-lock.json

@@ -1,7 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.18.0",
+  "version": "0.18.1",
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",
   "author": {