Fix Megatron-LM Arguments Bug

[yuanenming]

Bug fix: recompute_activation -> recompute_activations

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@pacman100

[pacman100]

Thank you @yuanenming for renaming a config param, but I don't think this is required. WIll leave it @muellerzr to decide regarding this.

[muellerzr]

Thanks for fixing! It is indeed recompute_activations and not recompute_activation

[HuggingFaceDocBuilderDev]

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