[release] package.json: remove 'preview' property

It was accidentally added during merge for v0.35.0

Fixes golang/vscode-go#2355
Fixes golang/vscode-go#2352

Change-Id: I50d4993fd2a6d2b84142c5db9ffc4a8aeda2c7cf
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/418194
Reviewed-by: Nooras Saba‎ <saba@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
diff --git a/package-lock.json b/package-lock.json
index 5c09230..347256c 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "go",
-  "version": "0.35.0",
+  "version": "0.35.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
diff --git a/package.json b/package.json
index 59e12fd..9884ac0 100644
--- a/package.json
+++ b/package.json
@@ -1,8 +1,7 @@
 {
   "name": "go",
   "displayName": "Go",
-  "version": "0.35.0",
-  "preview": true,
+  "version": "0.35.1",
   "publisher": "golang",
   "description": "Rich Go language support for Visual Studio Code",
   "author": {