Minor bug fixes on run_ner.py
Adding a dictionary entry outside of initialization requires an '=' instead of ':'
# [Codecov](https://codecov.io/gh/huggingface/transformers/pull/1918?src=pr&el=h1) Report
> Merging [#1918](https://codecov.io/gh/huggingface/transformers/pull/1918?src=pr&el=desc) into [master](https://codecov.io/gh/huggingface/transformers/commit/26db31e0c09a8b5e1ca7a61c454b159eab9d86be?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/1918/graphs/tree.svg?width=650&token=9qOlN6Hb1c&height=150&src=pr)](https://codecov.io/gh/huggingface/transformers/pull/1918?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master    #1918   +/-   ##
=======================================
  Coverage   84.04%   84.04%           
=======================================
  Files          97       97           
  Lines       14333    14333           
=======================================
  Hits        12046    12046           
  Misses       2287     2287
```



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<|||||>:+1:  sorry, that was a pasting mistake in https://github.com/huggingface/transformers/pull/1792 🙈