Maintain Dict Ordering with Concat
- [x] closes #21510
- [x] tests added / passed
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] whatsnew entry

although the set is instance of dict, it should not sort if it is also instance of OrderedDict
Hello @SaturninoMateus! Thanks for updating the PR.





Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on June 21, 2018 at 02:03 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=h1) Report
> Merging [#21512](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/506935c3482cb678b75dc7a70f48707c70b4ae79?src=pr&el=desc) will **increase** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/21512/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #21512      +/-   ##
==========================================
+ Coverage   91.92%   91.92%   +<.01%     
==========================================
  Files         153      153              
  Lines       49563    49566       +3     
==========================================
+ Hits        45559    45562       +3     
  Misses       4004     4004
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.32% <100%> (ø)` | :arrow_up: |
| #single | `41.8% <25%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/21512/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9jb25jYXQucHk=) | `97.61% <100%> (+0.02%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=footer). Last update [506935c...a7aa052](https://codecov.io/gh/pandas-dev/pandas/pull/21512?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Is this in reference to a particular issue? Sorry? What issue is this solving? Typically all pull requests (except for simple doc updates) refer to an issue on the issue tracker Issue #21510 OK thanks. For future PRs please add that reference in your original comment (I've updated it for you this time).

As per the checklist, you are also going to need tests and a whatsnew entry for 0.23.2 closing as stale, if you want to continue working, pls ping and we can re-open. you will need to merge master.