Cwltool doesn't recognise syntax sugar for array of arrays

Example tool:

```yaml
cwlVersion: v1.0
requirements:
ScatterFeatureRequirement: {}
class: Workflow
steps:
add:
run: add.cwl
in:
one: one
two: two
out: [sum]
scatter: [one, two]
scatterMethod: nested_crossproduct
inputs:
one: int[]
two: int[]
outputs:
sum:
outputSource: add/sum
type: int[][]
```

Gives error:

Field `type` references unknown identifier `int[][]`