Digger, I believe.
Disappointing.
Not sure if serious, but this is an issue that gets a disproportionate amount of outrage when it's suggested that it be changed, especially from the DM 'political correctness gone mad' gammon brigade. Any film, indeed any work of history, is going to involve choices about things to leave out or streamline; the dog itself is dramatically important, in that its death provides an ominous note of foreshadowing, and its name was the codeword for a successful mission, but the name is now so charged (and even then it wasn't exactly neutral, even if it was more commonplace) that to use it would overshadow the plot. I went to see the 1955 film in the Peckham multiplex back when it had a limited release about a decade ago, and the scene where Barnes Wallis is jumping around with joy shouting the name after the dams have been breached made me wince. Yes, it might be historically correct, but unless you want to raise (historically accurate) issues about British and Empire racism*, you probably just want to change the name.
*You never see the 'but it's historically accurate!' crowd calling for the film to better discuss the nature and morality of Bomber Command's campaign...