 */
 class Migrator_v1_v2: MigratorType {
     
-    internal let persistence: Persistence
+    internal var persistence: Persistence
     required init(persistence: Persistence) {
         self.persistence = persistence
     }


public protocol MigratorType {
    init(persistence: Persistence)
    var persistence: Persistence { get }
    func isMigrationRequired() -> Bool
    func attemptMigration() throws
}

*/
class Migrator_v0_v1: MigratorType {
    
    internal var persistence: Persistence
    required init(persistence: Persistence) {
        self.persistence = persistence
    }
