update main in package.json (#291)

* update main in package.json

* remove directories in package.json

Author: stevenjoezhang

package.json

@@ -2,7 +2,7 @@
   "name": "hexo-util",
   "version": "3.0.0",
   "description": "Utilities for Hexo.",
-  "main": "lib/index",
+  "main": "dist/index",
   "scripts": {
     "prepublishOnly": "npm install && npm run clean && npm run build",
     "build": "tsc -b",
@@ -15,10 +15,6 @@
     "build:highlight": "node scripts/build_highlight_alias.js",
     "prepare": "npm run build:highlight"
   },
-  "directories": {
-    "lib": "./lib",
-    "scripts": "./scripts"
-  },
   "files": [
     "dist/**",
     "scripts/",