Bump slim-rails from 3.1.2 to 3.1.3
Bump slim-rails from 3.1.2 to 3.1.3

Bumps [slim-rails](https://github.com/slim-template/slim-rails) from 3.1.2 to 3.1.3.
- [Release notes](https://github.com/slim-template/slim-rails/releases/tag/v3.1.3)
- [Changelog](https://github.com/slim-template/slim-rails/blob/master/CHANGELOG.md)
- [Commits](https://github.com/slim-template/slim-rails/compare/v3.1.2...v3.1.3)
kenchan/tdnm,kenchan/tdnm,kenchan/tdnm,kenchan/tdnm