**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
except json.decoder.JSONDecodeError:
                flash("Invalid JSON configuration", "error")
                return self.render_template(
                    'airflow/trigger.html',
                    dag_id=dag_id,
                    origin=origin,
                    conf=request_conf
                )
        dag = current_app.dag_bag.get_dag(dag_id)
        dag.create_dagrun(
            run_type=DagRunType.MANUAL,
            execution_date=execution_date,
            state=State.RUNNING,
            conf=run_conf,
            external_trigger=True,
        )
        flash(
            "Triggered {}, "
            "it should start any moment now.".format(dag_id))
        return redirect(origin)
    def _clear_dag_tis(self, dag, start_date, end_date, origin,
                       recursive=False, confirmed=False, only_failed=False):
        if confirmed:
            count = dag.clear(
                start_date=start_date,
                end_date=end_date,
                include_subdags=recursive,
                include_parentdag=recursive,
                only_failed=only_failed,
            )