Fix incorrect variable for linter standards

Summary: It is currently not possible to apply multiple linter standards because $value was used instead of $standard.

Test Plan: Was able to apply multiple linter standards.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: eadler, thaiphv, Korvin

Differential Revision: https://secure.phabricator.com/D15212