scripts/check_rabbitmq_connections lacks execution bit

Lintian gives the follow error:

```
Now running lintian...
W: nagios-plugins-rabbitmq: script-not-executable usr/lib/nagios/plugins-rabbitmq/check_rabbitmq_connections
N: 
N:    This file starts with the #! sequence that marks interpreted scripts,
N:    but it is not executable.
N:    
N:    Severity: normal, Certainty: certain
N:    
N:    Check: scripts, Type: binary
N: 
Finished running lintian.
```

This fork fixes this (small) issue.

Thanks