Fix height of DarkConsole request log

Summary: When I have displayed DarkConsole and write a comment it keeps scrolling because new AJAX requests pop up.

Test Plan: Displayed it, issued couple of AJAX requests.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T1316

Differential Revision: https://secure.phabricator.com/D3605