🚀 Add missing tokenizer test files

Several tokenizers currently have no associated tests. I think that adding the test file for one of these tokenizers could be a very good way to make a first contribution to transformers.

Tokenizers concerned

not yet claimed

• LED

• RemBert

• Splinter

• MobileBert

• ConvBert

• Electra

• RetriBert

claim

I opened jupyter notebook and openend the HTML.ipynb

I clicked on Cells>Run all

I waited for a while and then I got this result:

https://ibb.co/gRg3Z0n

If this can help I also got this message.

https://ibb.co/ZcbtH1N

How can I fix this so that I can generate the HTML code?

Thanks in advance

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  paddle版本2.0.8 paddlenlp版本2.1.0
  建议，能否在paddlenlp文档中，整理列出各个模型的tokenizer是基于什么类别的based，如bert tokenizer是word piece的，xlnet tokenizer是sentence piece的，以及对应的输入输出样例

The code would already produce charts in English. However, the current charts are in French.

One would need to try all the exercises to regenerate new charts, incorporate them in the notebook, and then regenerate the README in a clean way, as well as the .py file if the code in the notebook changed.

The French branch (which is named francais) should remain untouched.