**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
dep_context = DepContext(
            deps=RUNNING_DEPS,
            ignore_all_deps=ignore_all_deps,
            ignore_task_deps=ignore_task_deps,
            ignore_ti_state=ignore_ti_state)
        failed_deps = list(ti.get_failed_dep_statuses(dep_context=dep_context))
        if failed_deps:
            failed_deps_str = ", ".join(
                ["{}: {}".format(dep.dep_name, dep.reason) for dep in failed_deps])
            flash("Could not queue task instance for execution, dependencies not met: "
                  "{}".format(failed_deps_str),
                  "error")
            return redirect(origin)
        executor.start()
        executor.queue_task_instance(
            ti,
            ignore_all_deps=ignore_all_deps,
            ignore_task_deps=ignore_task_deps,
            ignore_ti_state=ignore_ti_state)
        executor.heartbeat()
        flash(
            "Sent {} to the message queue, "
            "it should start any moment now.".format(ti))
        return redirect(origin)
    @expose('/delete', methods=['POST'])
    @has_dag_access(can_dag_edit=True)
    @has_access
    @action_logging
    def delete(self):