Fix InputExample docstring
![image](https://user-images.githubusercontent.com/8499679/74761217-a1458700-5249-11ea-9fcf-0689c60ad5af.png)

# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/2891?src=pr&el=h1) Report
> Merging [#2891](https://codecov.io/gh/huggingface/transformers/pull/2891?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/2ae98336d17fceea7506af9880b862b6252a38f6?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/huggingface/transformers/pull/2891/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/2891?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #2891   +/-   ##
=======================================
  Coverage   75.06%   75.06%           
=======================================
  Files          94       94           
  Lines       15288    15288           
=======================================
  Hits        11476    11476           
  Misses       3812     3812
```


| [Impacted Files](https://codecov.io/gh/huggingface/transformers/pull/2891?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [src/transformers/data/processors/utils.py](https://codecov.io/gh/huggingface/transformers/pull/2891/diff?src=pr&el=tree#diff-c3JjL3RyYW5zZm9ybWVycy9kYXRhL3Byb2Nlc3NvcnMvdXRpbHMucHk=) | `21.73% <ø> (ø)` | :arrow_up: |

------

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<|||||>Thanks!<|||||>Thank you! Easiest review ever! Keep em coming :)