**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
"""View to show records from Variable table"""
    route_base = '/variable'
    list_template = 'airflow/variable_list.html'
    edit_template = 'airflow/variable_edit.html'
    datamodel = AirflowModelView.CustomSQLAInterface(models.Variable)  
    base_permissions = ['can_add', 'can_list', 'can_edit', 'can_delete', 'can_varimport']
    list_columns = ['key', 'val', 'is_encrypted']
    add_columns = ['key', 'val']
    edit_columns = ['key', 'val']
    search_columns = ['key', 'val']
    base_order = ('key', 'asc')
    def hidden_field_formatter(self):
        """Formats hidden fields"""
        key = self.get('key')  
        val = self.get('val')  
        if wwwutils.should_hide_value_for_key(key):
            return Markup('*' * 8)
        if val:
            return val
        else:
            return Markup('<span class="label label-danger">Invalid</span>')
    formatters_columns = {
        'val': hidden_field_formatter,
    }
    validators_columns = {
        'key': [validators.DataRequired()]
    }
    def prefill_form(self, form, request_id):