Bumps [actions/cache](https://github.com/actions/cache) from v1 to v2.1.5.
- [Release notes](https://github.com/actions/cache/releases)
- [Commits](https://github.com/actions/cache/compare/v1...1a9e2138d905efd099035b49d8b7a3888c653ca8)

Signed-off-by: dependabot[bot] <support@github.com>