Using retracted version v1.1.5 of hashicorp/go-msgpack

### Nomad version
`master`

### Operating system and Environment details
n/a
### Issue
The current version listed in `go.mod` is a retracted version, v1.1.5. Apparently version v2.0.0 is identical and should be used instead. This prevents updating to new versions of `github.com/hashicorp/nomad` in other projects (such as [github.com/hashicorp/terraform-provider-nomad](https://github.com/hashicorp/terraform-provider-nomad)
### Reproduction steps
Check `go.mod` file for `github.com/hashicorp/go-msgpack v1.1.5`
#### Expected Result
Find `github.com/hashicorp/go-msgpack v2.0.0` in `go.mod`
#### Actual Result
Find `github.com/hashicorp/go-msgpack v1.1.5` in `go.mod`

### Job file (if appropriate)

### Nomad Server logs (if appropriate)

### Nomad Client logs (if appropriate)

Open go.mod and locate the github.com/hashicorp/go-msgpack dependency. Confirm the current v1.1.5 entry and check that v2.0.0 is the intended replacement. Done means go.mod records v2.0.0 so downstream projects can update Nomad without using the retracted version.

Written by the indexing model from the issue text.