devel/phabricator: Bump minimum arcanist-lib dependency

This makes sure phabricator is using the Mozilla root CA bundle
when doing webhook calls (e.g., from harbormaster).

Before it would use the custom root CA bundle that shipped with
arcanist, which hasn't been updated in a while. This caused
problems with Let's Encrypt issued certificates, after the R3
Let's Encrypt intermediate CA expired.