Upgrade dependency

[hzxuzhonghu]

We haven't upgrade dependencies for long. It's time to do that, basically as k8s 1.18 has released. We must do that.

• K8s version, we should support k8s 1.15+ Test with go 1.13 and k8s 1.15 #63

• go version, support go 1.13 Test with go 1.13 and k8s 1.15 #63

• replace dep with go module Make use of go mod and bump k8s 1.18 #62