# 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.
underscore_replacement = '---'
    meta_header_prefix = 'x-amz-meta-'
    prefix_len = len(meta_header_prefix)
    updated = False
    for key in list(request_headers.keys()):
        if key.lower().startswith(meta_header_prefix):
            key_new = meta_header_prefix + key[prefix_len:].replace('_', underscore_replacement)
            if key != key_new:
                request_headers[key_new] = request_headers.pop(key)
                updated = True
    if response:
        for key in list(response.headers.keys()):
            if key.lower().startswith(meta_header_prefix):
                key_new = meta_header_prefix + key[prefix_len:].replace(underscore_replacement, '_')
                if key != key_new:
                    response.headers[key_new] = response.headers.pop(key)
    return updated
def fix_creation_date(method, path, response):