munin-master: Fix permissions to allow history_counters.json to be updated
Prior to this, the cron triggered to update the graph file history_counters.json failed silently.
This allows the cron to actually update the file successfully. In effect, allowing the graph from www.s.o/archive to be updated.
Test Plan
bin/octocatalog
Migrated from D1636 (view on Phabricator)