Fix parameter

http://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DescribeInstanceStatus.html  

shows that `InstanceId.N` does not suffixes `s` when passed as a parameter. 

Try running the following code and see the error message:

```go
// DescribeInstanceStatus describes EC2 instance status by instance ID.
func DescribeInstanceStatus(client *ec2.EC2, instanceID string) (ec2.InstanceStatusSet, error) {
	desc := ec2.DescribeInstanceStatus{
		InstanceIds:         []string{instanceID},
		IncludeAllInstances: true,
	}
	resp, err := client.DescribeInstanceStatus(&desc, ec2.NewFilter())
	if err != nil {
		return ec2.InstanceStatusSet{}, err
	}
	return resp.InstanceStatus[0], nil
}
```

`addParamsList(params, "InstanceIds", options.InstanceIds)` returns error message: 

```
The parameter InstanceIds is not recognized (UnknownParameter)
```

`addParamsList(params, "InstanceId", options.InstanceIds)` without `s` works, as expected.


Thanks!