ImportError: cannot import name 'HfArgumentParser' from 'transformers'
Hi! When running:

```
python ./examples/run_glue.py \
    --model_type bert \
    --model_name_or_path bert-base-uncased \
    --task_name $TASK_NAME \
    --do_train \
    --do_eval \
    --data_dir $GLUE_DIR/$TASK_NAME \
    --max_seq_length 128 \
    --per_gpu_eval_batch_size=8   \
    --per_gpu_train_batch_size=8   \
    --learning_rate 2e-5 \
    --num_train_epochs 3.0 \
    --output_dir /tmp/$TASK_NAME/

```

I get

```
Traceback (most recent call last):
  File "./examples/run_glue.py", line 34, in <module>
    from transformers import (
ImportError: cannot import name 'HfArgumentParser' from 'transformers' (/Users/leotreasure/opt/anaconda3/lib/python3.7/site-packages/transformers/__init__.py)

```

This is my python path
/Users/leotreasure/opt/anaconda3/bin/python

I ran the GLUE download script in the same folder
python download_glue_data.py
and exported: 
export GLUE_DIR=/Users/leotreasure/transformers
export TASK_NAME=MRPC
You need to install from source, as explained [here](https://github.com/huggingface/transformers#run-the-examples).<|||||>Thanks!