chore: use npm files instead of npmignore

ref: https://docs.npmjs.com/configuring-npm/package-json#files

package.json

@@ -3,6 +3,9 @@
   "version": "0.3.5",
   "description": "赫蹏是专为中文内容展示设计的排版样式增强。它基于通行的中文排版规范而来，可以为网站的读者带来更好的文章阅读体验。",
   "main": "lib/heti.scss",
+  "files": [
+    "dist/"
+  ],
   "directories": {
     "lib": "lib"
   },