Unknown task zero-shot-classification
Author: amarlearning
Pull request: no

## 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: Ubuntu 18
- Python version: 3.7

### Who can help
<!-- Your issue will be replied to more quickly if you can figure out the right person to tag with @
 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.
 
 albert, bert, GPT2, XLM: @LysandreJik 
 tokenizers: @mfuntowicz
 Trainer: @sgugger
 Speed and Memory Benchmarks: @patrickvonplaten
 Model Cards: @julien-c
 Translation: @sshleifer
 Summarization: @sshleifer
 TextGeneration: @TevenLeScao 
 examples/distillation: @VictorSanh
 nlp datasets: [different repo](https://github.com/huggingface/nlp)
 rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)
 Text Generation: @TevenLeScao
 blenderbot: @mariamabarham
 Bart: @sshleifer
 Marian: @sshleifer
 T5: @patrickvonplaten
 Longformer/Reformer: @patrickvonplaten
 TransfoXL/XLNet: @TevenLeScao 
 examples/seq2seq: @sshleifer
 tensorflow: @jplu 
documentation: @sgugger
 -->

## Information

Model I am using (Bert, XLNet ...):

The problem arises when using:
* [ ] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [ ] an official GLUE/SQUaD task: (give the name)
* [ ] my own task or dataset: (give details below)

## To reproduce

Steps to reproduce the behavior:

1. I downloaded transformer version 3.0.2
2. From transformer, I imported pipeline
3. And from the pipeline, I was trying to load this task `zero-shot-classification` and then I got the error.


<!-- If you have code snippets, error messages, stack traces please provide them here as well.
     Important! Use code tags to correctly format your code. See https://help.github.com/en/github/writing-on-github/creating-and-highlighting-code-blocks#syntax-highlighting
     Do not use screenshots, as they are hard to read and (more importantly) don't allow others to copy-and-paste your code.-->

```
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<ipython-input-12-1f0825594ce1> in <module>
----> 1 classifier = pipeline("zero-shot-classification")

~/anaconda3/lib/python3.7/site-packages/transformers/pipelines.py in pipeline(task, model, config, tokenizer, framework, **kwargs)
   1819     # Retrieve the task
   1820     if task not in SUPPORTED_TASKS:
-> 1821         raise KeyError("Unknown task {}, available tasks are {}".format(task, list(SUPPORTED_TASKS.keys())))
   1822 
   1823     framework = framework or get_framework(model)

KeyError: "Unknown task zero-shot-classification, available tasks are ['feature-extraction', 'sentiment-analysis', 'ner', 'question-answering', 'fill-mask', 'summarization', 'translation_en_to_fr', 'translation_en_to_de', 'translation_en_to_ro', 'text-generation']"
```

## Expected behavior

<!-- A clear and concise description of what you would expect to happen. -->


Comments:
Hello! this task is only available on the `master` branch as of now. You can install it as such: `pip install git+https://github.com/huggingface/transformers`.

It will be in the next release!

This is still happening on Databricks even though I re-installed the package several times today. Any thoughts?

@Tolga28A Can you document which exact command(s) you run on Databricks (and how)?

pip install git+https://github.com/huggingface/transformers
from transformers import pipeline
classifier = pipeline('zero-shot-classification')

and the output is:


KeyError: "Unknown task zero-shot-classification, available tasks are ['feature-extraction', 'sentiment-analysis', 'ner', 'question-answering', 'fill-mask', 'summarization', 'translation_en_to_fr', 'translation_en_to_de', 'translation_en_to_ro', 'text-generation']"
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
<command-2362828626522668> in <module>
----> 1 classifier = pipeline('zero-shot-classification')

/local_disk0/.ephemeral_nfs/envs/pythonEnv-a6d3a5c1-2f0b-495b-828f-f792f8695d17/lib/python3.7/site-packages/transformers/pipelines.py in pipeline(task, model, config, tokenizer, framework, **kwargs)
   1819     # Retrieve the task
   1820     if task not in SUPPORTED_TASKS:
-> 1821         raise KeyError("Unknown task {}, available tasks are {}".format(task, list(SUPPORTED_TASKS.keys())))
   1822 
   1823     framework = framework or get_framework(model)

KeyError: "Unknown task zero-shot-classification, available tasks are ['feature-extraction', 'sentiment-analysis', 'ner', 'question-answering', 'fill-mask', 'summarization', 'translation_en_to_fr', 'translation_en_to_de', 'translation_en_to_ro', 'text-generation']"

Start from a brand new venv or uninstall transformers before re-installing?