text: Title: Issue importing from txtai.pipeline
  Body: Hello there, I am trying to follow the example [here](https://neuml.github.io/txtai/pipeline/train/hfonnx/) in a Google Colab setup. I keep getting an error when I try to do any import such as 
  
  `from txtai.pipeline import xyz`
  
  In this case:
  
  `from txtai.pipeline import HFOnnx, Labels`
  
  Here's the end of the traceback I get:
  
  ```
  [<ipython-input-6-429aa8896e23>](https://localhost:8080/#) in <module>()
  ----> 1 from txtai.pipeline import HFOnnx, Labels
        2 
        3 # Model path
        4 path = "distilbert-base-uncased-finetuned-sst-2-english"
        5 
  
  [/usr/local/lib/python3.7/dist-packages/txtai/pipeline/__init__.py](https://localhost:8080/#) in <module>()
        8 from .factory import PipelineFactory
        9 from .hfmodel import HFModel
  ---> 10 from .hfpipeline import HFPipeline
       11 from .image import *
       12 from .nop import Nop
  
  [/usr/local/lib/python3.7/dist-packages/txtai/pipeline/hfpipeline.py](https://localhost:8080/#) in <module>()
        3 """
        4 
  ----> 5 from transformers import pipeline
        6 
        7 from ..models import Models
  
  /usr/lib/python3.7/importlib/_bootstrap.py in _handle_fromlist(module, fromlist, import_, recursive)
  
  [/usr/local/lib/python3.7/dist-packages/transformers/utils/import_utils.py](https://localhost:8080/#) in __getattr__(self, name)
      845             value = self._get_module(name)
      846         elif name in self._class_to_module.keys():
  --> 847             module = self._get_module(self._class_to_module[name])
      848             value = getattr(module, name)
      849         else:
  
  [/usr/local/lib/python3.7/dist-packages/transformers/utils/import_utils.py](https://localhost:8080/#) in _get_module(self, module_name)
      859             raise RuntimeError(
      860                 f"Failed to import {self.__name__}.{module_name} because of the following error (look up to see its traceback):\n{e}"
  --> 861             ) from e
      862 
      863     def __reduce__(self):
  
  RuntimeError: Failed to import transformers.pipelines because of the following error (look up to see its traceback):
  module 'PIL.Image' has no attribute 'Resampling'
  ```
  
  I'm not sure what I am doing wrong, but I tried installing following the example in the [notebook](https://colab.research.google.com/github/neuml/txtai/blob/master/examples/18_Export_and_run_models_with_ONNX.ipynb) which was:
  
  `pip install datasets git+https://github.com/neuml/txtai#egg=txtai[pipeline]`
  
  I also tried the following:
  
  `pip install datasets txtai[all]`