title: Writing BSONBinary to MongoDB fails with reactivemongo
body: <p>I am trying to save data into the database of a binary type.
  The call is: </p>
  
  <pre><code>val query = BSONDocument("_id" -&gt; binId)
  val update = BSONDocument(
    "$inc" -&gt; BSONDocument(
      "fieldA" -&gt; 1L
    ))
  
  coll.update(query, update, GetLastError(), upsert = true)
  </code></pre>
  
  <p>where</p>
  
  <pre><code>binId = BSONBinary(id, UuidSubtype):
  </code></pre>
  
  <p>I get exception from reactivemongo that looks in log like this:</p>
  
  <pre><code>ERROR akka.remote.EndpointWriter ClusterSystem-akka.acto
  r.default-dispatcher-3 - Transient association error (association remains live)
  java.io.NotSerializableException: reactivemongo.bson.buffer.ArrayReadableBuffer
      at java.io.ObjectOutputStream.writeObject0(Unknown Source) ~[na:1.7.0_45]
  </code></pre>
  
  <p>Any hints would be very appreciated!</p>