**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
"""Get Dag details."""
        dag_id = request.args.get('dag_id')
        dag = current_app.dag_bag.get_dag(dag_id)
        title = "DAG details"
        root = request.args.get('root', '')
        states = (
            session.query(TaskInstance.state, sqla.func.count(TaskInstance.dag_id))
                   .filter(TaskInstance.dag_id == dag_id)
                   .group_by(TaskInstance.state)
                   .all()
        )
        active_runs = models.DagRun.find(
            dag_id=dag_id,
            state=State.RUNNING,
            external_trigger=False
        )
        return self.render_template(
            'airflow/dag_details.html',
            dag=dag, title=title, root=root, states=states, State=State, active_runs=active_runs)
    @expose('/rendered')
    @has_dag_access(can_dag_read=True)
    @has_access
    @action_logging
    def rendered(self):