hub.verify not in spec anymore, still required by hub on subscribe

I'm using flask_websub (https://readthedocs.org/projects/flask-websub/) as a subscriber for a wordpress multisite on which I've installed the pushpress plugin. Comparing websub drafts 0.3 (https://pubsubhubbub.github.io/PubSubHubbub/pubsubhubbub-core-0.3.html) and current 0.4 (https://www.w3.org/TR/websub/) it seems that parameter hub.verify is not required anymore at subscribe. The hub included in pushpress still looks for it (line 49 of https://github.com/Automattic/pushpress/blob/master/class-pushpress.php) returning 400 to any (up to date) client.
I'll probably hack my way around this client side to conform to current hub status, but the best option would still be updating the plugin's behavior.
I'm not very php savvy, but if someone's willing to hold my hand through a review and/or tests I could try a pull request.

Start in class-pushpress.php at line 49 and compare the subscription handling with the current WebSub 0.4 specification linked in the issue. Trace how the plugin validates subscription parameters and verify that an up-to-date client is no longer rejected with HTTP 400 because hub.verify is absent.

Written by the indexing model from the issue text.