[release] package.json: update version to v0.31.1

For #2060

Change-Id: Ie9db402fc8fb950b6d8b14e12adc525d107f888a
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/384174
Trust: Hyang-Ah Hana Kim <[email protected]>
Run-TryBot: Hyang-Ah Hana Kim <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Suzy Mueller <[email protected]>
TryBot-Result: kokoro <[email protected]>

Author: hyangah

package-lock.json

@@ -1,7 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.31.0",
+  "version": "0.31.1",
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",
   "author": {