Set chmod to 755 instead of 711 for web static directories

Summary:
A Forbidden was served, as nginx wasn't allowed to read
the content of directory, and so know if there is or not
an index.html page.

Test Plan: https://assets.dereckson.be/fonts should be world readable

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D1012