<!--- Verify first that your issue is not already reported on GitHub -->
<!--- Also test if the latest release and devel branch are affected too -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Explain the problem briefly below -->
In docker_swarm_service module in ansible, if we are specifying mount option as tmpfs, it is required to set src. But for docker service create, src is not supported for tmpfs.
##### ISSUE TYPE
- Bug Report

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
docker_swarm_service

##### ANSIBLE VERSION
<!--- Paste verbatim output from "ansible --version" between quotes -->
```paste below
ansible 2.8.4
  config file = /home/vani/Projects/voody/ansible/ansible.cfg
  configured module search path = ['/home/vani/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/local/lib/python3.6/dist-packages/ansible
  executable location = /usr/local/bin/ansible
  python version = 3.6.8 (default, Aug 20 2019, 17:12:48) [GCC 8.3.0]

```

##### CONFIGURATION
<!--- Paste verbatim output from "ansible-config dump --only-changed" between quotes -->
```paste below
ANSIBLE_NOCOWS(/home/user/Projects/ansible/ansible.cfg) = True
DEFAULT_STDOUT_CALLBACK(/home/user/Projects/ansible/ansible.cfg) = yaml
```

##### OS / ENVIRONMENT
<!--- Provide all relevant information below, e.g. target OS versions, network device firmware, etc. -->


##### STEPS TO REPRODUCE
<!--- Describe exactly how to reproduce the problem, using a minimal test-case -->

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can paste gist.github.com links for larger files -->

##### EXPECTED RESULTS
<!--- Describe what you expected to happen when running the steps above -->


##### ACTUAL RESULTS
<!--- Describe what actually happened. If possible run with extra verbosity (-vvvv) -->

<!--- Paste verbatim command output between quotes -->
```paste below

```

placement = task_template_data.get('Placement')
        if placement:
            ds.constraints = placement.get('Constraints')
            placement_preferences = []
            for preference in placement.get('Preferences', []):
                placement_preferences.append(
                    dict(
                        (key.lower(), value['SpreadDescriptor'])
                        for key, value in preference.items()
                    )
                )
            ds.placement_preferences = placement_preferences or None
        restart_policy_data = task_template_data.get('RestartPolicy')
        if restart_policy_data:
            ds.restart_policy = restart_policy_data.get('Condition')
            ds.restart_policy_delay = restart_policy_data.get('Delay')
            ds.restart_policy_attempts = restart_policy_data.get('MaxAttempts')
            ds.restart_policy_window = restart_policy_data.get('Window')
        raw_data_endpoint_spec = raw_data['Spec'].get('EndpointSpec')
        if raw_data_endpoint_spec:
            ds.endpoint_mode = raw_data_endpoint_spec.get('Mode')
            raw_data_ports = raw_data_endpoint_spec.get('Ports')
            if raw_data_ports:
                ds.publish = []
                for port in raw_data_ports:
                    ds.publish.append({
                        'protocol': port['Protocol'],
                        'mode': port.get('PublishMode', None),
                        'published_port': int(port['PublishedPort']),
                        'target_port': int(port['TargetPort'])