Fix username route for new "._-" usernames

Summary: We allow ".", "_" and "-" in usernames now, but not in the route.

Test Plan: Went to /p/.-_/, got 404'd at the route level before and now make it to the profile controller.

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran

Maniphest Tasks: T1348

Differential Revision: https://secure.phabricator.com/D2729