Incorrect implementation of the ExtensionArray API in tests
I believe that
https://github.com/pandas-dev/pandas/blob/0c65c57a279e755ab7093db925d1e580f9878dae/pandas/tests/extension/decimal/array.py#L48
should read
```python
        return cls(original.take(values))
```
Same as reported at https://github.com/ContinuumIO/cyberpandas/issues/33,  @TomAugspurger 