cbtransfer gen: generates JSON with body field called "min-value-size"

If you run cbtransfer (or cbworkloadgen) to generate JSON...

./cbtransfer gen:json=1 stdout:

Then the JSON looks like...

{"name": "850", "age": 42, "index": 850, "min_value_size": "0000000000"}

Instead, it should look like...

{"name": "850", "age": 42, "index": 850, "body": "0000000000"}