Re-added defauflt constructor to use DefaultConnection if no conenctionNameOrUrl is specified.
Re-added defauflt constructor to use DefaultConnection if no conenctionNameOrUrl is specified.

Malkiat-Singh/MongoDB.AspNet.Identity,InspectorIT/MongoDB.AspNet.Identity,MetSystem/MongoDB.AspNet.Identity,gautamsi/MongoDB.AspNet.Identity,jsheely/MongoDB.AspNet.Identity,GravityJack/MongoDB.AspNet.Identity