Bump rustup from 6f93cdc to 2ce2428

Bumps [rustup](https://github.com/rust-lang-nursery/rustup.rs) from `6f93cdc` to `2ce2428`.
- [Release notes](https://github.com/rust-lang-nursery/rustup.rs/releases)
- [Commits](rust-lang/rustup@6f93cdc...2ce2428)

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

Author: dependabot-preview[bot]