**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
#
#
#
#
import copy
import itertools
import json
import logging
import math
import socket
import traceback
from collections import defaultdict
from datetime import datetime, timedelta
from json import JSONDecodeError
from typing import Dict, List, Optional, Tuple
from urllib.parse import unquote, urlparse
import lazy_object_proxy
import nvd3
import sqlalchemy as sqla
from flask import (
    Markup, Response, current_app, escape, flash, jsonify, make_response, redirect, render_template, request,
    session as flask_session, url_for,
)
from flask_appbuilder import BaseView, ModelView, expose, has_access, permission_name
from flask_appbuilder.actions import action
from flask_appbuilder.models.sqla.filters import BaseFilter  
from flask_babel import lazy_gettext
from jinja2.utils import htmlsafe_json_dumps, pformat  
from pygments import highlight, lexers