Take a look at https://estafette.io, it is our CI system we built here in https://travix.com in order to have a suitable Kubernetes native CI system running.
It was based on drone.io first versions and got lots of improvements this last year!
I personally like it a lot in the way we use here in Travix as it really gives the developers a really easy to way to trigger deployments to any K8s clusters without having to write manifests, knowing which sidecars to run, how to inject secrets, ssl, or anything like this. Estafette and it's controllers handle everything for us.
Feel free to ping me at twitter.com/armand1m if you're keen to know more about it =)