Update Kubeflow's Published Roadmap to include the 1.5 Release

[jbottum]

The Kubeflow Roadmap should be updated to reflect our plans for Kubeflow 1.5. /assign @jbottum

[jbottum]

Here is the current roadmap: https://github.com/kubeflow/kubeflow/blob/master/ROADMAP.md

[jbottum]

/closed