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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description
When I call the Lambda PutFunctionEventInvokeConfig API using the aws-java-sdk, the sdk throws an exception claiming it cannot parse the LastModified timestamp in the response:
```
software.amazon.awssdk.core.exception.SdkClientException: Unable to parse date : 2021-05-28T16:02:30.018Z
        at software.amazon.awssdk.core.exception.SdkClientException$BuilderImpl.build(SdkClientException.java:98)
        at software.amazon.awssdk.protocols.core.StringToInstant.lambda$safeParseDate$0(StringToInstant.java:77)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:54)
        at software.amazon.awssdk.protocols.core.StringToInstant.convert(StringToInstant.java:32)
```

For comparison, the response for a getting a FunctionEventInvokeConfig for a Lambda of a real AWS account using the aws-cli is the following:
```
{
    "LastModified": "2021-05-27T19:26:43.454000-07:00",
    "FunctionArn": "...",
    ...
}
```

## Expected behavior
LambdaAsyncClient in aws-java-sdk should correctly parse the response for a PutFunctionEventInvokeConfig request.

## Actual behavior
LambdaAsyncClient in aws-java-sdk throws an exception when parsing the LastModified field in the response.

# Steps to reproduce

## Command used to start LocalStack
```
docker run -d --rm --name localstack -p 4566:4566 localstack/localstack:latest
```

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)
```
val putEventInvokeConfigRequest =
  PutFunctionEventInvokeConfigRequest.builder
    .functionName(functionName)
    .maximumEventAgeInSeconds(21600)
    .maximumRetryAttempts(0)
    .build
lambdaClient.putFunctionEventInvokeConfig(putEventInvokeConfigRequest)
```


if name not in region.lambdas.get(arn).aliases:
        return not_found_error(msg='Alias not found: %s:%s' % (arn, name))
    return jsonify(region.lambdas.get(arn).aliases.get(name))
@app.route('%s/functions/<function>/aliases' % PATH_ROOT, methods=['GET'])
def list_aliases(function):
    region = LambdaRegion.get()
    arn = func_arn(function)
    if arn not in region.lambdas:
        return not_found_error(arn)
    return jsonify({'Aliases': sorted(region.lambdas.get(arn).aliases.values(),
                                      key=lambda x: x['Name'])})
@app.route('/<version>/functions/<function>/concurrency', methods=['GET', 'PUT', 'DELETE'])
def function_concurrency(version, function):
    region = LambdaRegion.get()
    
    
    
    arn = func_arn(function)
    lambda_details = region.lambdas.get(arn)
    if not lambda_details:
        return not_found_error(arn)
    if request.method == 'GET':
        data = lambda_details.concurrency
    if request.method == 'PUT':
        data = json.loads(request.data)
        lambda_details.concurrency = data
    if request.method == 'DELETE':
        lambda_details.concurrency = None
        return Response('', status=204)
    return jsonify(data)