**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
return wwwutils.json_response({})
        payload = {}
        dag_state_stats = dag_state_stats.filter(dr.dag_id.in_(filter_dag_ids))  
        data = {}
        for dag_id, state, count in dag_state_stats:
            if dag_id not in data:
                data[dag_id] = {}
            data[dag_id][state] = count
        for dag_id in filter_dag_ids:
            payload[dag_id] = []
            for state in State.dag_states:
                count = data.get(dag_id, {}).get(state, 0)
                payload[dag_id].append({
                    'state': state,
                    'count': count
                })
        return wwwutils.json_response(payload)
    @expose('/task_stats', methods=['POST'])
    @has_access
    @provide_session
    def task_stats(self, session=None):
        """Task Statistics"""
        allowed_dag_ids = set(current_app.appbuilder.sm.get_accessible_dag_ids())
        if not allowed_dag_ids:
            return wwwutils.json_response({})
        if 'all_dags' in allowed_dag_ids:
            allowed_dag_ids = {dag_id for dag_id, in session.query(models.DagModel.dag_id)}
        
        selected_dag_ids = {
            unquote(dag_id) for dag_id in request.form.getlist('dag_ids') if dag_id