Fix cpplint message regex
Summary:
ref T8404
The issue is caused, not by the non-zero return code, but by the fact that
$messages is coming back empty due to the incorrect regex. tyhoff pointed out
that the regex matched correctly when we used STDIN, but now it is failing.
Test Plan:
arc lint cpp file containing lint error. run cpplint on the
file directly to confirm that there are errors and that the return code
is non-zero
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: Korvin
Maniphest Tasks: T8404
Differential Revision: https://secure.phabricator.com/D14960