**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 'failed'"""
        self.set_task_instance_state(tis, State.FAILED)
        self.update_redirect()
        return redirect(self.get_redirect())
    @action('set_success', "Set state to 'success'", '', single=False)
    @has_dag_access(can_dag_edit=True)
    def action_set_success(self, tis):
        """Set state to 'success'"""
        self.set_task_instance_state(tis, State.SUCCESS)
        self.update_redirect()
        return redirect(self.get_redirect())
    @action('set_retry', "Set state to 'up_for_retry'", '', single=False)
    @has_dag_access(can_dag_edit=True)
    def action_set_retry(self, tis):
        """Set state to 'up_for_retry'"""
        self.set_task_instance_state(tis, State.UP_FOR_RETRY)
        self.update_redirect()
        return redirect(self.get_redirect())
class DagModelView(AirflowModelView):
    """View to show records from DAG table"""
    route_base = '/dagmodel'
    datamodel = AirflowModelView.CustomSQLAInterface(DagModel)  
    base_permissions = ['can_list', 'can_show']
    list_columns = ['dag_id', 'is_paused', 'last_scheduler_run',
                    'last_expired', 'scheduler_lock', 'fileloc', 'owners']
    formatters_columns = {
        'dag_id': wwwutils.dag_link
    }
    base_filters = [['dag_id', DagFilter, lambda: []]]
    def get_query(self):