Update Diviner for array-valued @doc-stuff return values from DocblockParser

Summary: Ref T11575. After D16431, the parser may return arrays.

Test Plan: Ran bin/diviner generate --clean in phabricator/ without errors. Previously, this raised some parsing errors related to getting arrays where strings were expected.

Reviewers: chad, yelirekim, joshuaspence

Reviewed By: joshuaspence

Maniphest Tasks: T11575

Differential Revision: https://secure.phabricator.com/D16487