Upgrade kube dependency to support GKE & macOS

[glyn]

Is your feature request related to a problem? Please describe.
make run fails on macOS with a GKE cluster:

make run
RUST_LOG="rudr=debug,kube=info" RUST_BACKTRACE=short cargo run
    Finished dev [unoptimized + debuginfo] target(s) in 0.32s
     Running `target/debug/rudr`
[2020-01-30T13:39:37Z INFO  rudr] starting server
[2020-01-30T13:39:37Z INFO  rudr] apiserver:https://34.65.118.77
[2020-01-30T13:39:37Z ERROR rudr] Error prechecking CRDs applicationconfigurations: Error { inner: Error(Hyper(Error(Connect, Custom { kind: Other, error: Error { code: -67843, message: "The certificate was not trusted." } })), "https://34.65.118.77/apis/apiextensions.k8s.io/v1beta1/customresourcedefinitions/applicationconfigurations.core.oam.dev")

Describe the solution you'd like
make run should work ok on macOS with a GKE cluster.

The easiest way is to upgrade kube to pick up kube-rs/kube@2b50f01.

Describe alternatives you've considered
I could use another cluster type, but I'm more comfortable with GKE. Also, this project will eventually need to upgrade kube, so it's only a matter of time.

Additional context
See technosophos/rust-k8s-controller#3 for a similar upgrade.

[ryanzhang-oss]

Thanks, Glyn, I wonder if you can submit a PR?

[glyn]

Thanks, Glyn, I wonder if you can submit a PR?

I'm afraid I won't have the time. When I attempted a quick upgrade, there were over 100 compilation errors.