Fix iconNav in Windows

Summary: Fixes T8012. The line height here with the stock Segoe font are causing some overflow issues. I guess Segoe bleeds out of the line-height bounding box.

Test Plan: Test Chrome, IE on Windows, Chrome on Mac. Seems spiffy to me.

Reviewers: btrahan, epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T8012

Differential Revision: https://secure.phabricator.com/D12646