I'm using Python wrappers for CDK to create a Glue job. The `command` attribute requires an object of type `IResolvable | Job­Command­Property`. I tried to put a `JobCommandProperty` object here but I'm getting an exception.

I created a `JobCommandProperty` object. I was looking for a `.builder()`function somewhere (similar than in the Java API), but couldn't find one.

```py
from aws_cdk import (
    aws_glue as glue,
    aws_iam as iam,
    core
)

class ScheduledGlueJob (core.Stack):

    def __init__(self, scope: core.Construct, id: str, **kwargs) -> None:
        super().__init__(scope, id, **kwargs)

        policy_statement = iam.PolicyStatement(
                actions=['logs:*','s3:*','ec2:*','iam:*','cloudwatch:*','dynamodb:*','glue:*']
            )

        policy_statement.add_all_resources()

        glue_job_role = iam.Role(
            self,
            'Glue-Job-Role',
            assumed_by=iam.ServicePrincipal('glue.amazonaws.com')
        ).add_to_policy(
            policy_statement
        )

        job = glue.CfnJob(
            self,
            'glue-test-job',
            role=glue_job_role,
            allocated_capacity=10,
            command=glue.CfnJob.JobCommandProperty(
                name='glueetl',
                script_location='s3://my-bucket/glue-scripts/job.scala'
            ))

```

The error message is this:

```
$cdk synth
Traceback (most recent call last):
  File "app.py", line 30, in <module>
    glue_job = ScheduledGlueJob(app, 'Cronned-Glue-Job')
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/jsii/_runtime.py", line 66, in __call__
    inst = super().__call__(*args, **kwargs)
  File "/Users/d439087/IdeaProjects/ds/test_cdk/glue/scheduled_job.py", line 33, in __init__
    script_location='s3://my-bucket/glue-scripts/job.scala'
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/jsii/_runtime.py", line 66, in __call__
    inst = super().__call__(*args, **kwargs)
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/aws_cdk/aws_glue/__init__.py", line 2040, in __init__
    jsii.create(CfnJob, self, [scope, id, props])
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/jsii/_kernel/__init__.py", line 208, in create
    overrides=overrides,
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/jsii/_kernel/providers/process.py", line 331, in create
    return self._process.send(request, CreateResponse)
  File "/Users/d439087/IdeaProjects/ds/test_cdk/.env/lib/python3.7/site-packages/jsii/_kernel/providers/process.py", line 316, in send
    raise JSIIError(resp.error) from JavaScriptError(resp.stack)
jsii.errors.JSIIError: Expected 'string', got true (boolean)

```

Maybe someone has a working CDK (python) example to create a `CfnJob`object?