Improve error message from ArcanistXHPASTLinter::LINT_FORMATTED_STRING
Improve error message from ArcanistXHPASTLinter::LINT_FORMATTED_STRING

Summary: Currently the error message from `ArcanistXHPASTLinter::LINT_FORMATTED_STRING` is slightly wrong, mentioning `xsprintf` instead of the actual `sprintf`-style function which was used. This diff changes the error message to be more correct.

Test Plan: Linted a file containing `sprintf('%s')` and saw a reasonable lint message.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12871

julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist,julkiewicz/arcanist