transformers.PreTrainedTokenizer.tokenize does lower case work all the time and discards space and tab. Want this changed.
# 🐛 Bug

## Information

Model I am using (Bert, XLNet ...):'albert_xxlarge_zh'

Language I am using the model on (English, Chinese ...):Chinese

Two problems are all related to method `transformers.PreTrainedTokenizer.tokenize`:

1. How can I not let this method automatically lower the case of the English words in the input sentence? `tokenizer.init_kwargs["do_lower_case"]=True` doesn't work...
2. How can I not let this method discard '\t' and space in default? Or is there any method that can solve this problem?

## To reproduce

Steps to reproduce the behavior:

`
tokenizer=BertTokenizer.from_pretrained("./albert_pytorch/prev_trained_model/albert_xxlarge_zh/")`
`print(tokenizer.init_kwargs.get("do_lower_case")) #output None`
`tokenizer.init_kwargs["do_lower_case"]=True`
`print(tokenizer.init_kwargs.get("do_lower_case")) #output True`
`seq=tokenizer.tokenize("我喜欢\tAPP和WIFI。")`
`print(seq)
`

## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->
Expected output is:
['我', '喜', '欢',**'\t'**, **'APP'**, '和', **'WIFI'**, '。']
While the actual output is:
['我', '喜', '欢', **'app'**, '和', **'wifi'**, '。']

## Environment info
<!-- You can run the command `python transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version:2.5.1
- Platform:ubuntu
- Python version:3.6.1
- PyTorch version (GPU?):1.1.0 cuda9
- Using GPU in script?:nope
- Using distributed or parallel set-up in script?:nope


**BTW**, `python transformers-cli env` didn't work, the callback :

> python: can't open file 'transformers-cli': [Errno 2] No such file or directory
This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.
