build: add files field to package.json

Author: cossssmin

package.json

@@ -34,5 +34,8 @@
     "np": "^7.0.0",
     "c8": "^7.12.0",
     "xo": "^0.53.1"
-  }
+  },
+  "files": [
+    "lib/*"
+  ]
 }