Direct type declaration fails isPrivate

[voliva]

If you declare an schema such as:

var userSchema = new Schema({
    username: String,
_password: String
})

That's perfectly valid for mongoose, toJSON will show the field _password because it's not detected properly in isPrivate method.

Atm, this is the ifthat fails:

else if(_.isObject(node) && !node.type && !node.getters) {

since node is the type String (internally that's a function) and underscore returns isObject as true.

Maybe the solution is like

else if(_.isObject(node) && !_.isFunction(node) && !node.type && !node.getters) {

[yamadapc]

Yeah... I'll think of something, thanks for the report! A PR would be greatly appreciated, since I'm not that free on time at the moment.