WriteObject to only take individual items

Overriding WriteObject shouldn't be concerned if it is a single item or an arrray.

Source/Schema.NET/ValuesJsonConverter.cs

@@ -138,7 +138,13 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
             }
             else
             {
-                this.WriteObject(writer, values.Cast<object>(), serializer);
+                writer.WriteStartArray();
+                foreach (var item in values)
+                {
+                    this.WriteObject(writer, item, serializer);
+                }
+
+                writer.WriteEndArray();
             }
         }