Bump miniz-sys from 0.1.11 to 0.1.12 (#607)

Bumps [miniz-sys](https://github.com/alexcrichton/flate2-rs) from 0.1.11 to 0.1.12.
- [Release notes](https://github.com/alexcrichton/flate2-rs/releases)
- [Commits](rust-lang/flate2-rs@miniz-sys-0.1.11...miniz-sys-0.1.12)

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