it doesn’t seem to be the iframe itself. that works on my test site when I paste in your code in the text mode of the editor.
Make sure you’re in text mode.
By the way, you should be on WP 4.5.3 now.
Thanks for the quick response! I know I was in text mode. Let me look into updating WP.
Edit: As of 13:19, I went to update my version of WP under the “Updates” section of the Dashboard. It’s showing that everything is up to date, so there is no way for me to update anything. I clicked “Check Again” and still have nothing available for an update.