**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 selected_dag_ids:
            filter_dag_ids = selected_dag_ids.intersection(allowed_dag_ids)
        else:
            filter_dag_ids = allowed_dag_ids
        
        running_dag_run_query_result = (
            session.query(DagRun.dag_id, DagRun.execution_date)
                   .join(DagModel, DagModel.dag_id == DagRun.dag_id)
                   .filter(DagRun.state == State.RUNNING, DagModel.is_active)
        )
        
        
        if selected_dag_ids:
            running_dag_run_query_result = \
                running_dag_run_query_result.filter(DagRun.dag_id.in_(filter_dag_ids))
        
        running_dag_run_query_result = running_dag_run_query_result.subquery('running_dag_run')
        
        
        running_task_instance_query_result = (
            session.query(TaskInstance.dag_id.label('dag_id'), TaskInstance.state.label('state'))
                   .join(running_dag_run_query_result,
                         and_(running_dag_run_query_result.c.dag_id == TaskInstance.dag_id,
                              running_dag_run_query_result.c.execution_date == TaskInstance.execution_date))
        )
        if selected_dag_ids:
            running_task_instance_query_result = \
                running_task_instance_query_result.filter(TaskInstance.dag_id.in_(filter_dag_ids))