Update MIGRATION.md (jobcloud#44)

* Update MIGRATION.md

* remove phpdbg

Author: nick-zh

MIGRATION.md

@@ -6,11 +6,11 @@ messaging systems than Kafka.
 
 In most cases you can just:
 1. `composer remove jobcloud/messaging-lib`
-2. `composer require jobcloud/php-kafka-lib ~0.1`
+2. `composer require jobcloud/php-kafka-lib ~0.1` (after migration, consider switching to the most current release)
 3. Replace namespace `Jobcloud\Messaging\Kafka` with `Jobcloud\Kafka`
 4. Replace the following:
  - `ConsumerException` with `KafkaConsumerConsumeException`
  - `MessageInterface` with `KafkaMessageInterface` or depending on your use case with `KafkaConsumerMessageInterface` and `KafkaProducerMessageInterface`
  - `ProducerInterface` with `KafkaProducerInterface`
  - `ConsumerInterface` with `KafkaConsumerInterface`
- - `ProducerPool` is not supported anymore
+ - `ProducerPool` is not supported anymore