As mongo go driver README show, it support MongoDB 2.6 or higher version.

In out enviroment, we use mongodb 2.6.12 which should be supported by mongo go driver.

However when we migrate from mgo to mongo go driver, we found a thing different is that:

• mgo support `dropDups` index option
• mongo go driver not support `dropDups` index option

I known `dropDups` option is deprecated from MongoDB 2.7.5 version, however this index option still exists in MongoDB 2.6, and mongo go driver desclared it support mongodb 2.6。

So we think it maybe a bug for mongo go driver，it should add `dropDups` index option back。