Release v3.0.0 to make the new major release importable

Without appropriate tagging it's still not possible to use semantic imports.

```console
github.com/kubernetes-csi/csi-test/v3/pkg/sanity: module github.com/kubernetes-csi/csi-test/v3@latest (v3.0.0-20191106140151-d305288bda09) found, but does not contain package github.com/kubernetes-csi/csi-test/v3/pkg/sanity
```