Move type generation from prepack to prepare

Author: aomarks

package.json

@@ -43,7 +43,7 @@
     "lint": "gulp lint",
     "generate-types": "gen-typescript-declarations --outDir . --deleteExisting --verify",
     "regen-package-lock": "rm -rf node_modules package-lock.json; npm install",
-    "prepack": "npm run generate-types"
+    "prepare": "npm run generate-types"
   },
   "repository": {
     "type": "git",