Fix tree view if config contains " (#9250)

Khrol · web-flow · commit a8cd23c8f04c · 2020-06-15T11:08:34.000+01:00
If you run DAG with `{"\"": ""}` configuration tree view will be broken:
```
tree:1 Uncaught SyntaxError: Unexpected string in JSON at position 806
    at JSON.parse (&lt;anonymous&gt;)
    at tree?dag_id=hightlight_test&amp;num_runs=25:1190
```

JSON.parse is given incorrectly escaped json string.
diff --git a/airflow/www/templates/airflow/tree.html b/airflow/www/templates/airflow/tree.html
@@ -136,7 +136,7 @@
 
 var devicePixelRatio = window.devicePixelRatio || 1;
 // JSON.parse is faster for large payloads than an object literal (because the JSON grammer is simpler!)
-var data = JSON.parse('{{ data }}');
+var data = JSON.parse({{ data|tojson }});
 var barHeight = 20;
 var axisHeight = 40;
 var square_x = parseInt(500 * devicePixelRatio);
