Upgrade dependencies

Summary:
Through npm outdated, syncing with upstream and checking npm,
dependencies with updates have been identified.

The imagemin process now handle SVG, GIF and PNG. For JPEG, mozjpeg
supersedes jpegtran.

Dart Saas supersedes node-sass, as the reference SCSS implementation.

To make YAML loading safer, optional types like regexps
are extracted to a separate js-yaml-js-types package.

Test Plan:
npm start
gulp build --production
npm outdated, npm audit

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2932