[release/1.1] Update tokio, rayon, and crossbeam to latest compatible…

… versions (#6135)

crossbeam-utils recently patched an unsoundness bug in `AtomicCell` arithmetic: crossbeam-rs/crossbeam#781. However, this patch was not backported to the older versions required by tokio 0.1 and rayon. This PR updates tokio and rayon to the latest available versions to unify our crossbeam dependencies, in particular unifying crossbeam-util to version 0.7.2. In the process, we can verify that we are not affected by the unsoundness bug by attempting a build with crossbeam-util patched to remove AtomicCell arithmetic.

## Azure IoT Edge PR checklist:

This checklist is used to make sure that common guidelines for a pull request are followed.

### General Guidelines and Best Practices
- [x] I have read the [contribution guidelines](https://github.com/azure/iotedge#contributing).
- [x] Title of the pull request is clear and informative.
- [x] Description of the pull request includes a concise summary of the enhancement or bug fix.

### Testing Guidelines
- [ ] Pull request includes test coverage for the included changes.
- Description of the pull request includes 
	- [ ] concise summary of tests added/modified
	- [x] local testing done.