Fix for typings error in postinstall script

Author: bsalex

package.json

@@ -13,7 +13,7 @@
     "watch": "webpack-dev-server --host 0.0.0.0",
     "build": "webpack",
     "lint": "tslint ./source/*.ts",
-    "postinstall": "typings install"
+    "prepare-development": "typings install"
   },
   "author": "Oleksandr Beshchuk <[email protected]>",
   "license": "Apache-2.0",