**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
datamodel = AirflowModelView.CustomSQLAInterface(models.DagRun)  
    base_permissions = ['can_list', 'can_add']
    add_columns = ['state', 'dag_id', 'execution_date', 'run_id', 'external_trigger', 'conf']
    list_columns = ['state', 'dag_id', 'execution_date', 'run_id', 'run_type', 'external_trigger', 'conf']
    search_columns = ['state', 'dag_id', 'execution_date', 'run_id', 'run_type', 'external_trigger', 'conf']
    base_order = ('execution_date', 'desc')
    base_filters = [['dag_id', DagFilter, lambda: []]]
    add_form = edit_form = DagRunForm
    formatters_columns = {
        'execution_date': wwwutils.datetime_f('execution_date'),
        'state': wwwutils.state_f,
        'start_date': wwwutils.datetime_f('start_date'),
        'dag_id': wwwutils.dag_link,
        'run_id': wwwutils.dag_run_link,
    }
    @action('muldelete', "Delete", "Are you sure you want to delete selected records?",
            single=False)
    @has_dag_access(can_dag_edit=True)
    @provide_session
    def action_muldelete(self, items, session=None):  
        """Multiple delete."""
        self.datamodel.delete_all(items)
        self.update_redirect()
        dirty_ids = []
        for item in items:
            dirty_ids.append(item.dag_id)
        return redirect(self.get_redirect())
    @action('set_running', "Set state to 'running'", '', single=False)
    @provide_session
    def action_set_running(self, drs, session=None):