# Type of request: This is a bug report

# Detailed description
S3 list buckets returns a different format for CreationDate than the one expected by the Java SDK and parsing fails. Using Java SDK 2.13.39. Also verified w/ .40, .38, .30 and .20. Will check previous Docker releases for localstack.

``Unable to unmarshall response (Text '2020-06-17T15:26:46.032838+00:00' could not be parsed at index 19). Response Code: 200, Response Text: 
software.amazon.awssdk.core.exception.SdkClientException: Unable to unmarshall response (Text '2020-06-17T15:26:46.032838+00:00' could not be parsed at index 19). Response Code: 200, Response Text: <truncated...>
``

## Expected behavior
Return CreationDate in same format as the actual S3 API call.

## Actual behavior
Returns CreationDate in slightly different format from the actual S3 API call. Fractional seconds are included.

# Steps to reproduce
Run "aws s3api list-buckets" vs "aws s3api list-buckets --endpoint-url http://localstack:4566" and note different date format for CreationDate.

## Command used to start LocalStack
docker-compose:
```
  localstack:
    image: localstack/localstack
    ports:
      - '4566:4566'
    environment:
      SERVICES: s3
      DEBUG: 1
```
## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
See steps to reproduce.
if method == 'PUT' and parsed.query == 'policy':
            response._content = ''
            response.status_code = 204
            return response
        
        if method == 'GET' and response.status_code == 404 and parsed.query != 'website':
            s3_client = aws_stack.connect_to_service('s3')
            try:
                
                s3_client.head_bucket(Bucket=bucket_name)
                website_config = s3_client.get_bucket_website(Bucket=bucket_name)
                error_doc_key = website_config.get('ErrorDocument', {}).get('Key')
                if error_doc_key:
                    error_object = s3_client.get_object(Bucket=bucket_name, Key=error_doc_key)
                    response.status_code = 200
                    response._content = error_object['Body'].read()
                    response.headers['Content-Length'] = str(len(response._content))
            except ClientError:
                
                pass
        if response is not None:
            reset_content_length = False
            
            append_cors_headers(bucket_name, request_method=method, request_headers=headers, response=response)
            append_last_modified_headers(response=response)
            append_list_objects_marker(method, path, data, response)
            fix_location_constraint(response)
            fix_range_content_type(bucket_name, path, headers, response)
            fix_delete_objects_response(bucket_name, method, parsed, data, headers, response)