Fix run_bertology.py
Make imports and `args.overwrite_cache` match `run_glue.py`.
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1765?src=pr&el=h1) Report
> Merging [#1765](https://codecov.io/gh/huggingface/transformers/pull/1765?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/1c542df7e554a2014051dd09becf60f157fed524?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/1765/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1765?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #1765   +/-   ##
=======================================
  Coverage   84.03%   84.03%           
=======================================
  Files          94       94           
  Lines       14032    14032           
=======================================
  Hits        11792    11792           
  Misses       2240     2240
```



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<|||||>That looks great, thanks @adrianbg !