{ optional: true } doesn't generate deeply-nested optional props in shapes

[markalfred]

shape = {
  shapeProp: PropTypes.shape({
    optionalProp: PropTypes.any,
    requiredProp: PropTypes.any.isRequired
  })
}

generateProps(shape, { optional: true })

// Expected:
{ shapeProp: { optionalProp: 'any', requiredProp: 'any' } }

// Actual: 
{ shapeProp: { requiredProp: 'any' } }

Note to self: likely that shape generator isn't forwarding opts to recursive generateProps calls.

[neil-morrison44]

This causes another issue too - nested objects use the default generators rather than the ones supplied in opts