Tokenizers Notebook  Issue
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Hello everyone,
While playing around with tokenizers notebook : https://github.com/huggingface/transformers/blob/master/notebooks/01-training-tokenizers.ipynb

`---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
 in 
----> 1 tokenizer = Tokenizer(BPE()) # byte-pair encoding model
      2 # now using normalizers
      3 tokenizer.normalizer = Sequence([
      4     NFKC(),
      5     Lowercase()

TypeError: cannot create 'BPE' instances`

Could not find a resolution for this.  thanks
pip version of installation has a problem, dependencies are not defined so it installs tokenizers-0.5.2 with transformers 2.8.0. 
Download from source and don't care warning of dependency, works fine :) 