Replaces deprecated DynomoDbClient’s formatAttribute function

[adonix]

1. The DynomoDbClient::formatAttributes function has been deprecated and its suggested fix is to use the function marshalItem from AWS DynomoDb’s Marshaler class.
2. When upgrading to AWS SKD PHP V3, it forces to update guzzle, which in turn will use the AWS Result class that now returns two items in its array: item and @metadata. Thus, fixed DynamoDb::ClientCredentials() to not use $result->count() == 1 anymore. However, this fix is still compatible with AWS SDK PHP V2 since it will use guzzle's common Collection class:

public function hasKey($key) { return array_key_exists($key, $this->data); }