title: failed with error 10068: "invalid operator: $oid"
body: <p>just updated to the latest version of mongoid (3.1.0) and sidekiq (2.7.2)<br>
  now i'm getting the error : <code>failed with error 10068: "invalid operator: $oid"</code><br>
  from looking into the code i see a select like that: <code>@selector={"_id"=&gt;{"$oid"=&gt;"[some id]"}}</code> <br>
  what can get wrong here?</p>