fix files package.json entry to be an array

Author: TSMMark

package.json

@@ -5,7 +5,7 @@
   "browser": "lib/index.js",
   "main": "lib/index.js",
   "module": "src/index.js",
-  "files": "lib/**/*",
+  "files": ["lib/"],
   "scripts": {
     "lint": "./node_modules/.bin/eslint src/.",
     "lint-fix": "npm run lint -- --fix",