Fix appointment insertion in database

src/appointment.php

@@ -63,6 +63,7 @@
                 <button class="create_btn" type="submit" name="create" >Añadir cita</button>
                 <?php $doctor = fetchDoctor($pdo); ?>
                 <input type="hidden" name="doctor" value="<?php echo $doctor; ?>">
+                <input type="hidden" name="fecha" id="fecha">
             </form>
             <?php closeDatabase($pdo); ?>
         </div>