Error #exists? is not implemented for Aws::IAM::User

`bundle update`

```
Installing aws-sdk-core 2.1.0 (was 2.0.31)
Installing aws-sdk-resources 2.1.0 (was 2.0.31)
Installing aws-sdk 2.1.0 (was 2.0.31)
```

``` ruby
iam = Aws::IAM::Client.new(region: 'eu-central-1')
user = Aws::IAM::User.new(name: 'xxxxx', client: iam)
user.exists?
```

=> `#exists? is not implemented for Aws::IAM::User`
