Unable to report version

When attempting to retrieve the currently installed version of the EC2 Instance Connect CLI, I receive an error message:

```
% mssh --version
Invalid target
usage:
mssh [-t instance_id] [-u profile] [-z availability_zone] [-r region] [supported ssh flags] target [command]

target => [user@]instance_id | [user@]hostname
[supported ssh flags] => [-l login_name] [-p port]

options:
-h, --help show this help message and exit
-r , --region AWS region
-z , --zone Availability zone
-u , --profile AWS Config Profile
-t , --instance_id EC2 Instance ID. Required if target is hostname
-d, --debug Turn on debug logging
```

I think it would be an improvement if the current version number were printed instead.