fix example

Before this change my schema save would never return. Reason:
Counter.findOne(..)'s callback was never called. I am using mongoose v3.6.20

Here is a change I had to make in my app to make this plugin work:
https://github.com/mkoryak/passthispipe.com/commit/2e7019621951256a342f4a77e5e07d7f68970bec