BUG: set_precision format fixed (#13257)
- [x] closes #13257
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

I've tried to fix the set_precision format, does that fix it? 

### INPUT -> df.style.set_precision(2)
| A | B |
| --- | --- |
| 1 | 2.0090 |
| 3.2121 | 4.566 |
### OUTPUT
| A | B |
| --- | --- |
| 1 | 2.01 |
| 3.21 | 4.57 |

@vinigl
@samuelgranato



Hello @AntonioAndraues! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-10-16 14:57:46 UTC Can you add a test for this > Can you add a test for this

I just added a test.
Is that it?  > Looks good. Can you add a release note to doc/source/whatsnew/v1.0.0.rst under "bug fixes"? Probably the "Other" section.

Done Thanks. Looks like there's a merge conflict in 1.0.0.rst, if you could fix that. > Thanks. Looks like there's a merge conflict in 1.0.0.rst, if you could fix that.
@TomAugspurger 
I think i fix it. CI is failing now. Do your tests need to be updated? > CI is failing now. Do your tests need to be updated?
@TomAugspurger 
I'm sorry forgot to update them... 
I think everything will be fine now!

 Hmm CI is still failing. Haven't taken a look though. > Hmm CI is still failing. Haven't taken a look though.
I think CI is failing because some test from others contributors are expecting the older use of style...
Do i change the test?
<img width="656" alt="Captura de Tela 2019-09-19 às 09 34 27" src="https://user-images.githubusercontent.com/26484794/65244445-ef026b80-dac0-11e9-8da3-c75e783f8576.png">
@TomAugspurger  If the old test is wrong then for sure should update @AntonioAndraues is this still active? If so can you fix up merge conflict? @WillAyd Yes. I Will fix it...
Sunday in the afternoon i commit it.  Great thanks @AntonioAndraues - nice PR! I _think_ this PR should be identified as a breaking change.

```python
import pandas as pd
pd.__version__
df = pd.DataFrame([0.1])
df
df.style.highlight_min()
```
in pandas 0.25.1
![image](https://user-images.githubusercontent.com/13159005/71480033-f5566100-27ee-11ea-89aa-016ae56e9b21.png)

on master
![image](https://user-images.githubusercontent.com/13159005/71479979-d2c44800-27ee-11ea-9f0b-868551a595c0.png)
