Don't atomize closures

Summary: In a PHP5.3+ codebase with closures, Diviner would pick up anonymous functions and add them into the generated documentation. This causes them to be skipped.

Test Plan: Ran bin/diviner generate --clean before and after change, no longer got a bunch of unnamed functions dumped into the documentation.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9786