Temporary hot fix in documentation

amqp-connection-manager was updated to version 4.0.0 3 days ago. It is not working well in case when connection is refused. Warning/error logs are absent. 
Version 3.9.0 of amqp-connection-manager is ok

Author: playka

content/microservices/rabbitmq.md

@@ -7,7 +7,7 @@
 To start building RabbitMQ-based microservices, first install the required packages:
 
 ```bash
-$ npm i --save amqplib amqp-connection-manager
+$ npm i --save amqplib amqp-connection-manager@3.9.0
 ```
 
 #### Overview