Option JsonSchema generation with jackson-module-jsonSchema

We have been trying to use [jackson-module-jsonSchema](https://github.com/FasterXML/jackson-module-jsonSchema) in combination with `jackson-module-scala` to generate JSON Schema from Scala case classes.

We have found it to work pretty well so far, however it doesn't render Options correctly. They come out as `{"type":"any"}`.

This pull request contains a failing test showing the problem. I don't have a fix and I don't know enough to be able to determine if this is a problem in `jackson-module-scala` or `jackson-module-jsonSchema`, but and happy to do some further digging if required.

    "...stringValue":{"type":"[any"]}}}" was not equal to "...stringValue":{"type":"[string","required":false]}}}" (OptionSerializerTest.scala:88)