[lib] Fix ESLint errors on lib/webpack/shared.cjs

Summary: In the parent diff we make ESLint work with .cjs files. This diff corrects the resultant errors.

Test Plan: eslint lib/webpack/shared.cjs

Reviewers: benschac

Reviewed By: benschac

Subscribers: palys-swm, Adrian, atul, karol-bisztyga, yayabosh

Differential Revision: https://phabricator.ashoat.com/D3834