Change double quotes to single quotes.

Summary: Ran `arc lint --apply-patches --everything` over rP, 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: Eyeballed it.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin, hach-que

Differential Revision: https://secure.phabricator.com/D9431

src/applications/phpast/controller/PhabricatorXHPASTViewPanelController.php

@@ -11,7 +11,7 @@ abstract class PhabricatorXHPASTViewPanelController
     $this->storageTree = id(new PhabricatorXHPASTViewParseTree())
       ->load($this->id);
     if (!$this->storageTree) {
-      throw new Exception("No such AST!");
+      throw new Exception('No such AST!');
     }
   }