Draw.io integration broke after an update to 0.30.2 #2313

Describe the bug
Since we updated Bookstack last week, we cant use draw.io.

We're using Markdown. The issue exists ONLY if your editor is Markdown.

Expected behavior
It opens the platform, but won't let us save the diagram.

Screenshots
If applicable, add screenshots to help explain your problem.

Your Configuration (please complete the following information):

• Exact BookStack Version (Found in settings): 0.30.2
• PHP Version: PHP 7.2.24-0ubuntu0.18.04.6 (cli) (built: May 26 2020 13:09:11) ( NTS )
• Hosting Method (Nginx/Apache/Docker): NGINX