Disable strict mode of JSON::Validator

Strict mode treats all properties as required, and ignores the
`required` attribute specified in the schema. This behaviour makes it
impossible to have optional fields in the schema.

Using the `required` property in the schema allows you to specify which
other properties are required and which are optional.
Merge pull request #8 from chrisrbnelson/master

Disable strict mode of JSON::Validator