OK ec2 api, what are the expected characters?

aal.rs

```
extern crate docopt;
extern crate rusoto;
extern crate awsshuf;
extern crate serde;
extern crate serde_json;


use rusoto::Region;
use rusoto::ec2::{Ec2Client, DescribeInstancesRequest};
use std::str::FromStr;
use docopt::Docopt;

const USAGE: &'static str = "
Query amazon for a random choice among some set of resources

Display matching resources as a json document.


Usage:
  aal [-c | --no-cache] [-a <api>...] [-r <region>...] <pattern>
  aal (-h | --help)

Options:
  -h --help                Show this screen
  -c --no-cache            Bypass the cached resources info
  -r --region=<region>     Region (can be specified more than once) [default: us-east-1 us-west-2]
  -a --api=<api>           Which AWS API, defaults to EC2
";



fn main() {
    let version = "0.1.0".to_owned();
    let parsed_cmdline = Docopt::new(USAGE)
        .and_then(|d| d.version(Some(version)).parse())
        .unwrap_or_else(|e| e.exit());
    println!("{:?}", parsed_cmdline);
    let creds = awsshuf::auth::credentials_provider(None, None);
    let r = parsed_cmdline.get_vec("-r");

    let reg = Region::from_str(r[0]).unwrap();
    let client = Ec2Client::new(creds, reg);
    let req = DescribeInstancesRequest::default();
    println!("{:?}", req);
    match client.describe_instances(&req) {
        Ok(response) => {
            println!("Got a response");
            println!("{:?}", response.reservations.unwrap()[0].instances);
        },
        Err(error) => {
            println!("Error: {:?}", error);
        }
    }
}
```

$ target/debug/aal .
-a, --api => List([])
-h, --help => Switch(false)
-c, --no-cache => Switch(false)
-r, --region => List(["us-east-1", "us-west-2"])
<pattern> => Plain(Some("."))
DescribeInstancesRequest { dry_run: None, filters: None, instance_ids: None, max_results: None, next_token: None }
Error: Unknown("Expected characters")