build(deps): bump error-chain from 0.12.3 to 0.12.4
build(deps): bump error-chain from 0.12.3 to 0.12.4

Bumps [error-chain](https://github.com/rust-lang-nursery/error-chain) from 0.12.3 to 0.12.4.
- [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/compare/0.12.3...0.12.4)

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
coreos/update-ssh-keys,coreos/update-ssh-keys