require wp-hooks-js for iframe, it's needed now with the changes in #12

[joshfeck]

Problem this Pull Request solves

Calendar iFrame no longer loads with the new version of the calendar add-on. This is the error in the console: Uncaught ReferenceError: wp is not defined Related PR #12

How has this been tested

Activate calendar add-on, then go to {site url}?calendar=iframe Calendar should populate events as expected

Checklist

• [x] I have read the documentation relating to systems affected by this pull request, see https://github.com/eventespresso/event-espresso-core/tree/master/docs
• [x] User input is adequately validated and sanitized
• [x] all publicly displayed strings are internationalized (usually using esc_html__(), see https://codex.wordpress.org/I18n_for_WordPress_Developers)
• [x] My code is tested.
• [x] My code follows the Event Espresso code style.
• [x] My code has proper inline documentation.
• [x] My code accounts for when the site is in Maintenance Mode (MM2 especially disallows usage of models)