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# Type of request: This is a ...

[x] bug report
[ ] feature request

# Detailed description
VTL request containing an expression evaluated to String Concatenation does not work.

### Query
```
mutation createShop {
            createShop(shop: { shopName: "Apple" } ) {
              shopName
            }
          }
```

### VTL Template (**Works when deploy to Appsync on AWS services**)
```
{
  "version" : "2018-05-29",
  "operation" : "PutItem",
  "key" : {
    "PK": $util.dynamodb.toDynamoDBJson("SHOP#${ctx.args.shop.shopName}"),
    "SK": $util.dynamodb.toDynamoDBJson("PROFILE#$ctx.args.shop.shopName")
  },
  "attributeValues" : { "shopName": { "S": "Apple" }}
}
```

## Expected behavior
### Item stored in dynamodb 
```
{
            "PK": {
                "S": "SHOP#Apple"
            },
            "SK": {
                "S": "PROFILE#Apple"
            },
            "shopName": {
                "S": "Apple"
            }
        }
```


## Actual behavior
### Item stored in dynamodb 
```
{
            "PK": {
                "S": "SHOP#${ctx.args.shop.shopName}"
            },
            "SK": {
                "S": "PROFILE#$ctx.args.shop.shopName"
            },
            "shopName": {
                "S": "Apple"
            }
        }
```

# Steps to reproduce

## Command used to start LocalStack
docker-compose
````
version: '2.1'

services:
  localstack:
    container_name: "${LOCALSTACK_DOCKER_NAME-localstack_main}"
    image: localstack/localstack
    ports:
      - "4566-4700:4566-4700"
      - "443:443"
      - "${PORT_WEB_UI-8080}:${PORT_WEB_UI-8080}"
    environment:
      - SERVICES=serverless,cloudformation,dynamodb,iam,s3,appsync,edge
      - DEBUG=1
      - DATA_DIR=${DATA_DIR- }
      - PORT_WEB_UI=${PORT_WEB_UI- }
      - LAMBDA_EXECUTOR=${LAMBDA_EXECUTOR- }
      - KINESIS_ERROR_PROBABILITY=${KINESIS_ERROR_PROBABILITY- }
      - DOCKER_HOST=unix:///var/run/docker.sock
      - HOST_TMP_FOLDER=${TMPDIR}
      - LOCALSTACK_API_KEY=${LOCALSTACK_API_KEY}
    volumes:
      - "${TMPDIR:-/tmp/localstack}:/tmp/localstack"
      - "/var/run/docker.sock:/var/run/docker.sock"
````

## Client code (AWS SDK code snippet, or sequence of "awslocal" commands)

...

for lib in libs:
        paths = [lib, '%s.py' % lib]
        try:
            module = importlib.import_module(lib)
            paths.append(module.__file__)
        except Exception:
            pass
        target_dir = tmp_dir
        root_folder = os.path.join(LOCALSTACK_VENV_FOLDER, 'lib/python*/site-packages')
        if lib == 'localstack':
            paths = ['localstack/*.py', 'localstack/utils']
            root_folder = LOCALSTACK_ROOT_FOLDER
            target_dir = os.path.join(tmp_dir, lib)
            mkdir(target_dir)
        for path in paths:
            file_to_copy = path if path.startswith('/') else os.path.join(root_folder, path)
            for file_path in glob.glob(file_to_copy):
                name = os.path.join(target_dir, file_path.split(os.path.sep)[-1])
                if os.path.isdir(file_path):
                    copy_dir(file_path, name)
                else:
                    shutil.copyfile(file_path, name)
    
    result = create_zip_file(tmp_dir, get_content=get_content)
    return result
def delete_lambda_function(name):
    client = aws_stack.connect_to_service('lambda')
    client.delete_function(FunctionName=name)
def create_zip_file_cli(source_path, base_dir, zip_file):