Bump tslib from 2.2.0 to 2.3.1 (#261)
Bump tslib from 2.2.0 to 2.3.1 (#261)

Bumps [tslib](https://github.com/Microsoft/tslib) from 2.2.0 to 2.3.1.
- [Release notes](https://github.com/Microsoft/tslib/releases)
- [Commits](https://github.com/Microsoft/tslib/compare/2.2.0...2.3.1)
benjamn/optimism,benjamn/optimism