fix: reduces tarball size

Author: nexdrew

package.json

@@ -55,5 +55,8 @@
     "mocha": "^2.4.5",
     "nyc": "^6.1.1",
     "standard": "^6.0.8"
-  }
+  },
+  "files": [
+    "index.js"
+  ]
 }