fix(stub): correct how we are getting db in migration

Author: RomainLanz

stubs/migration.stub

@@ -8,14 +8,14 @@ import { QueueSchemaService } from '@boringnode/queue'
 
 export default class extends BaseSchema {
   async up() {
-    const schemaService = new QueueSchemaService(this.db.connection().getWriteClient())
+    const schemaService = new QueueSchemaService(this.db.getWriteClient())
 
     await schemaService.createJobsTable()
     await schemaService.createSchedulesTable()
   }
 
   async down() {
-    const schemaService = new QueueSchemaService(this.db.connection().getWriteClient())
+    const schemaService = new QueueSchemaService(this.db.getWriteClient())
 
     await schemaService.dropSchedulesTable()
     await schemaService.dropJobsTable()