Changed the version of MOPED to HEAD (2.*)

This implementation works with the new Moped 2.*, the test was 'Failing' because you can't search with String, you have to search with BSON::ObjectId.from_string(id_string)
The purpose of this test is to ensure we can pass a string id to the query (so we don't have to convert from a string to a `BSON::ObjectId` if the id is read from a place that doesn't supply an actual object, but instead just a string (like a Rails request). This line shouldn't change.