title: DeprecationWarning: Listening to events on the Db class has been deprecated and will be removed in the next major version
body: <p>I am using mongoose and mocha for MongoDB schema design and API development
  I am getting this warning...
  what does this mean, how it will affect me and what is the fix??</p>
  <p>Below the actual warning text:</p>
  <blockquote>
  <p>(node:9872) DeprecationWarning: Listening to events on the Db class has been deprecated and will be removed in the next major version.</p>
  </blockquote>