ExecuteScalarAsync not supported

[ihsansfd]

This one important method in Dapper isn't checked in the switch case. Please consider adding a mock for this method, as I'm using this and postponed testing it. Probably I'm going to use a wrapper, unless the library got updated and the method got supported.

Update: just noticed that it's only missing in the interface IDbConnection, but for the concrete class DbConnection it's implemented. But I need it for the interface, not concrete class.