Move tail to <body>
Summary:
Prevents invalid HTML.
Discussion at D1561#6.
Test Plan:
http://validator.w3.org/check?uri=https%3A%2F%2Fsecure.phabricator.com
Reviewers: epriestley
Reviewed By: epriestley
CC: aran, epriestley
Differential Revision: https://secure.phabricator.com/D1563