**Apache Airflow version**:

master

**Kubernetes version (if you are using kubernetes)** (use `kubectl version`):

**Environment**: breeze

**What happened**:

This DAG
```python
from airflow import models
from airflow.operators.dummy_operator import DummyOperator
from airflow.utils.dates import days_ago

with models.DAG("test", start_date=days_ago(1), schedule_interval=None,) as dag:
    t1 = DummyOperator(task_id="t1")
    t2 = DummyOperator(task_id="t2")
    t1 >> t2
```

is rendering like that:

<img width="1374" alt="Screenshot 2020-08-27 at 19 59 41" src="https://user-images.githubusercontent.com/9528307/91478403-11d7fb00-e8a0-11ea-91d0-d7d578bcb5a2.png">

**What you expected to happen**:

I expect to see same relations as defined in DAG file

**How to reproduce it**:

Render the example DAG from above.


**Anything else we need to know**:

I'm surprised by this bug 👀 

airflow/www/views.py
"""
        An endpoint helping check the health status of the Airflow instance,
        including metadatabase and scheduler.
        """
        payload = {
            'metadatabase': {'status': 'unhealthy'}
        }
        latest_scheduler_heartbeat = None
        scheduler_status = 'unhealthy'
        payload['metadatabase'] = {'status': 'healthy'}
        try:
            scheduler_job = SchedulerJob.most_recent_job()
            if scheduler_job:
                latest_scheduler_heartbeat = scheduler_job.latest_heartbeat.isoformat()
                if scheduler_job.is_alive():
                    scheduler_status = 'healthy'
        except Exception:  
            payload['metadatabase']['status'] = 'unhealthy'
        payload['scheduler'] = {'status': scheduler_status,
                                'latest_scheduler_heartbeat': latest_scheduler_heartbeat}
        return wwwutils.json_response(payload)
    @expose('/home')
    @has_access
    def index(self):