Change double quotes to single quotes.
Summary: Ran arc lint --apply-patches --everything over rPHU, mainly to change double quotes to single quotes where appropriate. These changes also validate that the ArcanistXHPASTLinter::LINT_DOUBLE_QUOTE rule is working as expected.
Test Plan: arc unit --everything and eyeballed the diff.
Reviewers: epriestley, #blessed_reviewers
Reviewed By: epriestley, #blessed_reviewers
Subscribers: epriestley, Korvin
Differential Revision: https://secure.phabricator.com/D9184