R1:b5518d4bfb0d

fix a typo in troubleshooting perf wiki page

Summary: Fix typo. That said, I love the example.

Test Plan: no

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D15210