**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
"""Set state to success."""
        try:
            count = 0
            dirty_ids = []
            altered_tis = []
            for dr in session.query(DagRun).filter(
                    DagRun.id.in_([dagrun.id for dagrun in drs])).all():  
                dirty_ids.append(dr.dag_id)
                count += 1
                altered_tis += \
                    set_dag_run_state_to_success(current_app.dag_bag.get_dag(dr.dag_id),
                                                 dr.execution_date,
                                                 commit=True,
                                                 session=session)
            altered_ti_count = len(altered_tis)
            flash(
                "{count} dag runs and {altered_ti_count} task instances "
                "were set to success".format(count=count, altered_ti_count=altered_ti_count))
        except Exception:  
            flash('Failed to set state', 'error')
        return redirect(self.get_default_url())
class LogModelView(AirflowModelView):
    """View to show records from Log table"""
    route_base = '/log'
    datamodel = AirflowModelView.CustomSQLAInterface(Log)  
    base_permissions = ['can_list']