Fix support for #merge accepting either one object, multiple objects, or an array of objects.
Fix support for #merge accepting either one object, multiple objects, or an array of objects.

virajsanghvi/seamless-immutable,jedwards1211/seamless-immutable,SamHowie/seamless-immutable,rtfeldman/seamless-immutable,oliverwoodings/seamless-immutable,crudh/seamless-immutable