Misspelled property in README.md#marshaller-groups

[ctkdev]

Misspelled property in README.md#marshaller-groups

README.md#marshaller-groups

The declaration of a 'defaultJSON' group in marshallerGroups with the keyword 'groups' is incorrect. Using, 'group' does work.

`
restfulApiConfig = {

marshallerGroups {

    groups 'defaultJSON' marshallers {

    marshaller {

        instance = new net.hedtech.restulfapi.marshallers.json.DateMarshaller()

        priority = 100

    }

    marshaller {

        instance = new net.hedtech.restulfapi.marshallers.json.AddressMarshaller(grailsApplication)

        priority = 100

    }

}

`