How to stop cwltool to download $schemas (is there way full ignore?)

## Expected Behavior
--skip-schemas - I believe has to skip to download them

I use --non-strict --skip-schemas

## Actual Behavior
Schema salad still downloads it

## Workflow Code
```
$namespaces:
s: http://schema.org/

$schemas:
- http://schema.org/docs/schema_org_rdfa.html

s:name: "bowtie-index"
s:downloadUrl: https://raw.githubusercontent.com/SciDAP/workflows/master/dummy/bowtie-index.cwl
s:codeRepository: https://github.com/SciDAP/workflows
s:license: http://www.apache.org/licenses/LICENSE-2.0

s:isPartOf:
class: s:CreativeWork
s:name: Common Workflow Language
s:url: http://commonwl.org/
s:creator:
- class: s:Organization
s:legalName: "Cincinnati Children's Hospital Medical Center"
s:location:
- class: s:PostalAddress
s:addressCountry: "USA"
s:addressLocality: "Cincinnati"
s:addressRegion: "OH"

```

## Full Traceback
```pytb
Field `$schemas` contains undefined reference to `http://schema.org/docs/schema_org_rdfa.html`
../../../../usr/local/lib/python3.6/site-packages/biowardrobe_cwl_workflows/workflows/bowtie-index.cwl:81:5: checking item
../../../../usr/local/lib/python3.6/site-packages/biowardrobe_cwl_workflows/workflows/bowtie-index.cwl:81:5: Field `class` contains undefined reference to `http://schema.org/PostalAddress`
WARNI [salad] ../../../../usr/local/lib/python3.6/site-packages/biowardrobe_cwl_workflows/workflows/bowtie-index.cwl:81:5: checking item
../../../../usr/local/lib/python3.6/site-packages/biowardrobe_cwl_workflows/workflows/bowtie-index.cwl:81:5: Field `class` contains undefined reference to `http://schema.org/PostalAddress`
```

## Your Environment
* cwltool version: 1.0.20180912090223