Change the mode of the directory created by PhutilKeyValueCacheDirectory

Summary: Change the mode of the directory created by PhutilKeyValueCacheDirectory from 0777 to 0755. In general, this directory shouldn't need g+x or o+x permissions.

Test Plan: Ran diviner generate and checked the permissions on the .divinercache directory.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9947