Allows migrator.options.logging to be set to false

Previously, this would cause an exception to be thrown:
```
Uncaught TypeError: Property 'logging' of object #<Object> is not a function
      at module.exports.Migrator.migrate (sequelize/lib/migrator.js:58:26)
      at module.exports.Migrator.getUndoneMigrations (sequelize/lib/migrator.js:146:25)
      at EventEmitter.emit (events.js:88:17)
      at module.exports.CustomEventEmitter.emit (sequelize/lib/emitters/custom-event-emitter.js:61:33)
      at module.exports.Migrator.getLastMigrationIdFromDatabase (sequelize/lib/migrator.js:264:19)
      at EventEmitter.emit (events.js:88:17)
      at module.exports.CustomEventEmitter.emit (sequelize/lib/emitters/custom-event-emitter.js:61:33)
      at module.exports.Migrator.getLastMigrationFromDatabase (sequelize/lib/migrator.js:245:23)
      at EventEmitter.emit (events.js:88:17)
      at module.exports.CustomEventEmitter.emit (sequelize/lib/emitters/custom-event-emitter.js:61:33)
      at module.exports.QueryInterface.queryAndEmit (sequelize/lib/query-interface.js:974:19)
      at EventEmitter.emit (events.js:88:17)
      at module.exports.CustomEventEmitter.emit (sequelize/lib/emitters/custom-event-emitter.js:61:33)
      at module.exports.onSuccess (sequelize/lib/dialects/sqlite/query.js:180:10)
      at Statement.module.exports.Query.run.database.serialize.executeSql (sequelize/lib/dialects/sqlite/query.js:52:25)
  --> in Database#all('SELECT * FROM `SequelizeMeta` ORDER BY id DESC LIMIT 1;', [Function])
      at module.exports.Query.run.database.serialize.executeSql (sequelize/lib/dialects/sqlite/query.js:43:54)
      at funcs (sequelize/node_modules/lodash/dist/lodash.js:5143:23)
      at Statement.module.exports.Query.run (sequelize/lib/dialects/sqlite/query.js:80:17)
```