Bump node-sass from 3.4.2 to 3.13.1
Bump node-sass from 3.4.2 to 3.13.1

Bumps [node-sass](https://github.com/sass/node-sass) from 3.4.2 to 3.13.1.
- [Release notes](https://github.com/sass/node-sass/releases)
- [Changelog](https://github.com/sass/node-sass/blob/master/CHANGELOG.md)
- [Commits](https://github.com/sass/node-sass/compare/3.4.2...v3.13.1)

---
updated-dependencies:
- dependency-name: node-sass
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
rob-murray/gb-geojson,rob-murray/gb-geojson