**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
if dag:
                
                max_active_runs = dag.max_active_runs
            payload.append({
                'dag_id': dag_id,
                'active_dag_run': active_dag_runs,
                'max_active_runs': max_active_runs,
            })
        return wwwutils.json_response(payload)
    def _mark_dagrun_state_as_failed(self, dag_id, execution_date, confirmed, origin):
        if not execution_date:
            flash('Invalid execution date', 'error')
            return redirect(origin)
        execution_date = timezone.parse(execution_date)
        dag = current_app.dag_bag.get_dag(dag_id)
        if not dag:
            flash('Cannot find DAG: {}'.format(dag_id), 'error')
            return redirect(origin)
        new_dag_state = set_dag_run_state_to_failed(dag, execution_date, commit=confirmed)
        if confirmed:
            flash('Marked failed on {} task instances'.format(len(new_dag_state)))
            return redirect(origin)
        else:
            details = '\n'.join([str(t) for t in new_dag_state])
            response = self.render_template(
                'airflow/confirm.html',
                message="Here's the list of task instances you are about to mark as failed",
                details=details)
            return response
    def _mark_dagrun_state_as_success(self, dag_id, execution_date, confirmed, origin):