Add package.json files field instead of .npmignore

Author: Normaltic

.npmignore

@@ -4,6 +4,10 @@
   "description": "React daum-postcode component",
   "main": "./lib/index.js",
   "types": "./index.d.ts",
+  "files": [
+    "lib",
+    "index.d.ts"
+  ],
   "scripts": {
     "build": "babel src -d lib",
     "test": "echo \"Error: no test specified\" && exit 1"