Error using pipeline with officiel docker image (transformers 3.0.2)
Author: ZeJ0hn
Pull request: no
Labels: name: wontfix

## Environment info
<!-- You can run the command `transformers-cli env` and copy-and-paste its output below.
     Don't forget to fill out the missing fields in that output! -->
     
- `transformers` version: 3.0.2
- Platform: Linux-4.19.76-linuxkit-x86_64-with-Ubuntu-18.04-bionic
- Python version: 3.6.9
- PyTorch version (GPU?): 1.5.1 (False)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: <fill in>
- Using distributed or parallel set-up in script?: <fill in>

## To reproduce

Steps to reproduce the behavior:

1. Start docker image: 
`docker run -it huggingface/transformers-pytorch-cpu /bin/bash`
2. Start python 3:
`python3`
3. Import transfomers and create the pipeline:
```
>>> from transformers import pipeline
>>> nlp = pipeline('question-answering')
```
4. Define question and context:
```
>>> question='What is the GOC at Zinia-1 ?'
>>> context='s. However numerous types of data tend to prove presence of oil i.e. mud gas data show C3 and traces of C4, shows on cuttings and oil was seen by LFA during MDT pump out The middle unit U4 1844-1880.5 MD is oil bearing. No gas is seen from logs at the assumed GOC depth within this unit flat spot at 1849 MD or -1830 TVDSS The lower unit U2 1880.5-1909 mMD is also oil bearing. Pressure data indicate that the 3 units are on-trend although the GWD gas while drilling result suggest barriers between the U2, U4 and U5 in addition to the ultimate seal. The oil sampled in the UM4 has higher viscosity than the oil collected. s. However numerous types of data tend to prove presence of oil i.e. mud gas data show C3 and traces of C4, shows on cuttings and oil was seen by LFA during MDT pump out The middle unit U4 1844-1880.5 MD is oil bearing. No gas is seen from logs at the assumed GOC depth within this unit flat spot at 1849 MD or -1830 TVDSS The lower unit U2 1880.5-1909 mMD is also oil bearing. Pressure data indicate that the 3 units are on-trend although the GWD gas while drilling result suggest barriers between the U2, U4 and U5 in addition to the ultimate seal. The oil sampled in the UM4 has higher viscosity than the oil collected'
```
5. Call the prediction for question answering:
```
>>> nlp(question=question, context=context, verbose=False)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/dist-packages/transformers/pipelines.py", line 1316, in __call__
    for s, e, score in zip(starts, ends, scores)
  File "/usr/local/lib/python3.6/dist-packages/transformers/pipelines.py", line 1316, in <listcomp>
    for s, e, score in zip(starts, ends, scores)
KeyError: 0
```

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## Expected behavior

Get the answer like this (this result comes from 2.11.0):
`{'score': 0.00025710496321816774, 'start': 300, 'end': 322, 'answer': '1849 MD or -1830 TVDSS'}`


Comments:
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