Update to newest gifski version

Lockfile

Bump error-chain from 0.12.0 to 0.12.1

Bumps [error-chain](https://github.com/rust-lang-nursery/error-chain) from 0.12.0 to 0.12.1.
- [Release notes](https://github.com/rust-lang-nursery/error-chain/releases)
- [Changelog](https://github.com/rust-lang-nursery/error-chain/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-lang-nursery/error-chain/commits)