Ignore differential files for export
Ignore differential files for export

Summary: Add .arcconfig and .arclint to .gitattributes

Test Plan: Read the patch

Reviewers: Legoktm

Reviewed By: Legoktm

Differential Revision: https://phabricator.wikimedia.org/D41

bd808/composer-merge-plugin,webflo/composer-merge-plugin,wikimedia/composer-merge-plugin,codeandcountry/composer-merge-plugin