refactor: update export

include defaultTags and srcset utils

Author: cossssmin

lib/index.js

@@ -179,4 +179,9 @@ const plugin = (options = {}) => tree => {
   return tree.walk(process)
 }
 
-export default plugin
+export {
+  plugin as default,
+  defaultTags,
+  parseSrcset,
+  stringifySrcset,
+}