**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 rendered Dag."""
        dag_id = request.args.get('dag_id')
        task_id = request.args.get('task_id')
        execution_date = request.args.get('execution_date')
        dttm = timezone.parse(execution_date)
        form = DateTimeForm(data={'execution_date': dttm})
        root = request.args.get('root', '')
        logging.info("Retrieving rendered templates.")
        dag = current_app.dag_bag.get_dag(dag_id)
        task = copy.copy(dag.get_task(task_id))
        ti = models.TaskInstance(task=task, execution_date=dttm)
        try:
            ti.get_rendered_template_fields()
        except AirflowException as e:  
            msg = "Error rendering template: " + escape(e)
            if e.__cause__:  
                msg += Markup("<br/><br/>OriginalError: ") + escape(e.__cause__)
            flash(msg, "error")
        except Exception as e:  
            flash("Error rendering template: " + str(e), "error")
        title = "Rendered Template"
        html_dict = {}
        for template_field in task.template_fields:
            content = getattr(task, template_field)
            if template_field in wwwutils.get_attr_renderer():
                html_dict[template_field] = wwwutils.get_attr_renderer()[template_field](content)
            else:
                html_dict[template_field] = \
                    Markup("<pre><code>{}</pre></code>").format(pformat(content))