bug in bert pretraining 
## Environment info
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     Don't forget to fill out the missing fields in that output! -->

- `transformers` version: 4.3.2
- Platform: linux
- Python version: 3.7 
- PyTorch version (GPU?): 1.7 
- Tensorflow version (GPU?): - 
- Using GPU in script?: - 
- Using distributed or parallel set-up in script?: - 

### Who can help
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Models:

- albert, bert, xlm: @LysandreJik
- blenderbot, bart, marian, pegasus, encoderdecoder,  t5: @patrickvonplaten, @patil-suraj
- longformer, reformer, transfoxl, xlnet: @patrickvonplaten
- fsmt: @stas00
- funnel: @sgugger
- gpt2: @patrickvonplaten, @LysandreJik
- rag: @patrickvonplaten, @lhoestq
- tensorflow: @jplu

Library:

- benchmarks: @patrickvonplaten
- deepspeed: @stas00
- ray/raytune: @richardliaw, @amogkam
- text generation: @patrickvonplaten
- tokenizers: @n1t0, @LysandreJik
- trainer: @sgugger
- pipelines: @LysandreJik

Documentation: @sgugger

HF projects:

- nlp datasets: [different repo](https://github.com/huggingface/nlp)
- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

Examples:

- maintained examples (not research project or legacy): @sgugger, @patil-suraj
- research_projects/bert-loses-patience: @JetRunner
- research_projects/distillation: @VictorSanh

 -->

- albert, bert, xlm: @LysandreJik

## Information

In this line https://github.com/huggingface/transformers/blob/e73a3e1891775a915846cc0f24b7e9a26d6688fb/src/transformers/data/data_collator.py#L381 you need to change 0.5 to 0.1 to match the description written that only in 10% you would like to change  tokens with randomly selected tokens. 


## To reproduce
Nothing to reproduce.

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## Expected behavior

probs should match BERT paper. 
Duplicate of https://github.com/huggingface/transformers/issues/10285