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. 

`addParamsList(params, "InstanceIds", options.InstanceIds)` returns error message: 

```
The parameter InstanceIds is not recognized (UnknownParameter)
```
Merge pull request #173 from gyuho/master

Fix parameter