LibJS: Add missing <AK/Function.h> include in JSONObject.cpp

Libraries/LibJS/Runtime/JSONObject.cpp

@@ -24,6 +24,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
+#include <AK/Function.h>
 #include <AK/JsonArray.h>
 #include <AK/JsonObject.h>
 #include <AK/JsonParser.h>