Cargo upgrade service project

Create a service that automatically upgrades Cargo dependencies

Background information: Servo depends on numerous other Rust libraries that are published on the package manager crates.io. There are no notifications for when packages are updated; it's up to developers to keep track of when they need to upgrade their dependencies. The goal of this project is to build a service similar to Greenkeeper that can automatically upgrade Servo's dependencies whenever new versions are released.

Initial steps: