Improve atomizing of PHP @return annotation
Summary: Fixes T6890. This doesn't feel like a perfect solution, but I can't think of any cases in which this will produce the wrong result either.
Test Plan: Ran ./bin/diviner generate and checked the generated documentation for PhabricatorCommonPasswords::loadWordlist(). The return type was corrected shown as map<string, bool>.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin, epriestley
Maniphest Tasks: T6890
Differential Revision: https://secure.phabricator.com/D11469