The parameter SriovNetSupport is not recognized (AWS::EC2::Errors::UnknownParameter)

I came across a bug when enabling SR-IOV on C3 instances.

```ruby
ec2.client.modify_instance_attribute(
  :instance_id => instance.id,
  :sriov_net_support => { :value => 'simple' },
)
```

```
/Users/yuuki/code/aws/vendor/bundle/ruby/2.0.0/bundler/gems/aws-sdk-ruby-464ef3f6d755/lib/aws/core/client.rb:366:in `return_or_raise': The parameter SriovNetSupport is not recognized (AWS::EC2::Errors::UnknownParameter)
	from /Users/yuuki/code/aws/vendor/bundle/ruby/2.0.0/bundler/gems/aws-sdk-ruby-464ef3f6d755/lib/aws/core/client.rb:467:in `client_request'
	from (eval):3:in `modify_instance_attribute'
	from ./bin/create_instance.rb:186:in `<main>'
```

HTTP request body.
```
AWSAccessKeyId=XXXXXXXXXXXXX&Action=ModifyInstanceAttribute&InstanceId=i-00hoge&Signature=XXXXXXXXXXXXXXXXXXXXX&SignatureMethod=HmacSHA256&SignatureVersion=2&SriovNetSupport.Value=simple&Timestamp=2013-12-03T06%3A40%3A03Z&Version=2013-10-01"
```

I think the specified API version is old...

I used the github latest version, so it seems that SR-IOV is supported because of https://github.com/aws/aws-sdk-ruby/commit/77085ad3993b58fb23f5c8cbce5dbe6f9b3bff1e.  
```
gem 'aws-sdk', :github => 'aws/aws-sdk-ruby', :ref => '464ef3f6d75560580d2fc8b10aebdb149e69d9f0'
```