remove preview tag from packages

Author: d-biehl

package.json

@@ -5,7 +5,6 @@
   "icon": "images/icon.png",
   "publisher": "d-biehl",
   "version": "0.5.1",
-  "preview": true,
   "author": {
     "name": "Daniel Biehl",
     "url": "https://github.com/d-biehl/"