Typo ionf example code

[ThomasWolf0701]

In the following code it reads generator = blood_yolo_generator,
but this has not been defined, so it should read train_blood_yolo_generator

blood_yolo %>%
fit_generator(
generator = blood_yolo_generator,
epochs = 1000,
steps_per_epoch = 19,
validation_data = valid_blood_yolo_generator,
validation_steps = 5,
callbacks = list(callback_model_checkpoint("development/BCCD/blood_w.hdf5",
save_best_only = TRUE,
save_weights_only = TRUE)
)
)