Fix undefined result
Fix undefined result

Mongodb 3.0 + Mongoose 4.1.0

in result (index.js:125): 

{ value: { _id: 'sclients', field: '_id', seq: 31 },
  lastErrorObject: { updatedExisting: true, n: 1 },
  ok: 1 }
mirrr/mongodb-autoincrement,TheRoSS/mongodb-autoincrement