Apply form iframe is too small when bonus information is requested (how an applicant heard about us)

[wslack]

This code sets the iframe height upon page load. Anyone who selects a recruitment source that asks a follow-up question (like who referred them) causes the iframe to expand without triggering a reset of the iframe size.

The result is that the "apply" button disappears at the bottom of the page, causing poor user experience for applicants unless they notice to scroll the iframe up.