rabbitmq: 3.2.4

rabbitmq-v3.2.4 has been released.

Also v3.2.3 file is missing, so installing v3.2.3 fail.
```
$ brew install rabbitmq
==> Downloading http://www.rabbitmq.com/releases/rabbitmq-server/v3.2.3/rabbitmq-server-mac-standalone-3.2.3.tar.gz

curl: (22) The requested URL returned error: 404 Not Found
Error: Failed to download resource "rabbitmq"
Download failed: http://www.rabbitmq.com/releases/rabbitmq-server/v3.2.3/rabbitmq-server-mac-standalone-3.2.3.tar.gz
```