[release-v0.42] extension/package.json: prepare for v0.42.1

For #3520

Change-Id: I158e22239d7c857c4117ac04463eef32ed9d30a2
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/612040
kokoro-CI: kokoro <[email protected]>
Commit-Queue: Hyang-Ah Hana Kim <[email protected]>
Reviewed-by: Hongxiang Jiang <[email protected]>

Author: hyangah

extension/package-lock.json

@@ -1,7 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.42.0",
+  "version": "0.42.1",
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",
   "author": {