Update finetune.yaml (facebookresearch#2664)

Summary:
Fix a typo

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- [ ] Was this discussed/approved via a Github issue? (no need for typos, doc improvements)
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- [ ] Did you make sure to update the docs?
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## What does this PR do?
Fixes # (issue).

## PR review
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Pull Request resolved: fairinternal/fairseq-py#2664

Reviewed By: alexeib

Differential Revision: D32577174

Pulled By: arbabu123

fbshipit-source-id: 9b65619843fd9684be319024ccc9e6b0681db7de

examples/wav2vec/xlsr/config/finetune.yaml

@@ -63,4 +63,4 @@ model:
   feature_grad_mult: 0.0
   freeze_finetune_updates: 10000
 
-  checkpoint_activation: false
+  checkpoint_activations: false