Bugfix: prepare command added.

package.json

@@ -20,6 +20,7 @@
     "url": "git://git.nibgat.space/nibgat-community/rrule.git"
   },
   "scripts": {
+    "prepare": "yarn build",
     "prebuild": "yarn clean",
     "prepublish": "yarn build",
     "build": "yarn lint && tsc -b tsconfig.build.json && webpack",