Have UuidInterface extend from JsonSerializable and cover it with a test

src/Uuid.php

@@ -35,7 +35,7 @@ use Ramsey\Uuid\Codec\CodecInterface;
  * @link http://docs.oracle.com/javase/6/docs/api/java/util/UUID.html
  */
 
-class Uuid implements UuidInterface, \JsonSerializable
+class Uuid implements UuidInterface
 {
     /**
      * When this namespace is specified, the name string is a fully-qualified domain name.

src/UuidInterface.php

@@ -16,7 +16,7 @@ namespace Ramsey\Uuid;
 
 use Ramsey\Uuid\Converter\NumberConverterInterface;
 
-interface UuidInterface
+interface UuidInterface extends \JsonSerializable
 {
 
     /**