Fix an issue where the profile menu could become enormous

Summary: Ref T10054. Without max-width, Safari can make this too large with a long project name (maybe because of table-cell?).

Test Plan: Saw normal-width menu instead of huge menu on very long project.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10054

Differential Revision: https://secure.phabricator.com/D15046