Invalid deployment gives warning --> returns code 1

kubeval version: 1.15

Using --ignore-missing-schemas for another file provides a "WARN", but gives return code 0

In our pipeline we recently got return code 1 with no "ERR" visible, making me confused. The return code stems from this file:

Not sure if this is expected or not? Seems odd to me, and should rather cast an Error instead of warning.

```
➜ sdp-flux git:(dev) ✗ /mnt/c/appl/kubeval dev/gitlabstats/deployment-patch.yaml
WARN - dev/gitlabstats/deployment-patch.yaml contains an invalid Deployment (monitoring.gitlabstats) - selector: selector is required
WARN - dev/gitlabstats/deployment-patch.yaml contains an invalid Deployment (monitoring.gitlabstats) - template: template is required
➜ sdp-flux git:(dev) ✗ printf '%d\n' $?
1
```

It was hard to spot for me atleast as our pipeline renders many files, and if none provide an error I would presume return code 0, and pipeline is green.