Break long words on txt files in Diffusion

Summary: Fixes T12163. We don't send txt files through a pygment highlighter, so the break-word needs to also just apply to diffusion-source.

Test Plan: Test in Chrome Inspector

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T12163

Differential Revision: https://secure.phabricator.com/D17303