Add some spacing below the last hint in Bibliotron
Add some spacing below the last hint in Bibliotron

Test Plan:
{F343251}
{F343252}

Reviewers: alex

Reviewed By: alex

Subscribers: #bibliotron

Differential Revision: https://phabricator.khanacademy.org/D25770

learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus