pybricks.hubs.EssentialHub: Rename buttons to button.

This was copied from the Prime Hub, but the Essential Hub has only one button, just like the City Hub and Technic Hub.

Author: laurensvalk

pybricks/hubs/pb_type_essentialhub.c

@@ -49,7 +49,7 @@ STATIC mp_obj_t hubs_EssentialHub_make_new(const mp_obj_type_t *type, size_t n_a
 
 STATIC const mp_rom_map_elem_t hubs_EssentialHub_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_battery), MP_ROM_PTR(&pb_module_battery)    },
-    { MP_ROM_QSTR(MP_QSTR_buttons), MP_ROM_ATTRIBUTE_OFFSET(hubs_EssentialHub_obj_t, buttons) },
+    { MP_ROM_QSTR(MP_QSTR_button), MP_ROM_ATTRIBUTE_OFFSET(hubs_EssentialHub_obj_t, buttons) },
     { MP_ROM_QSTR(MP_QSTR_imu), MP_ROM_ATTRIBUTE_OFFSET(hubs_EssentialHub_obj_t, imu) },
     { MP_ROM_QSTR(MP_QSTR_light), MP_ROM_ATTRIBUTE_OFFSET(hubs_EssentialHub_obj_t, light) },
     { MP_ROM_QSTR(MP_QSTR_system), MP_ROM_PTR(&pb_type_System) },