Importing github.com/coreos/go-oidc@master causes dependency conflicts

**Describe the bug**

If you write a Go program and import `github.com/cloudflare/cloudflared/token` to generate a CF access token, there is a good chance of running into unresolvable module conflicts.

For example, I have a program that already imports the current version of go-oidc using `github.com/coreos/go-oidc/v3`. The cloudflared module appears to depend on `github.com/coreos/go-oidc@master`. This conflicts with the go-oidc versions on both the v2 and v3 branches.

Maybe related to #167