Make it Entity Framework 6 RC1 compatible

An exception happens when using EF 6 RC1 at
```C#
BrockAllen.MembershipReboot.Ef.DbContextRepository`1.BrockAllen.MembershipReboot.IRepository<T>.Update(T item)
   at BrockAllen.MembershipReboot.EventBusRepository`1.Update(T item) in projects\BrockAllen.MembershipReboot\src\BrockAllen.MembershipReboot\Repository\EventBusRepository.cs:line 81
````
which is ```inner.Update(item);``` which calls the ```IRepository<T>.Update(T item)``` at DbContextRepository`1.cs:line 64