style: fix import format at pandas/core/reshape
- [ ] xref #23334
- [x] passes `git diff master -u -- "*.py" | flake8 --diff`

Hello @streeck! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/core/reshape/api.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/api.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/concat.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/concat.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/melt.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/melt.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/merge.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/merge.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/pivot.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/pivot.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/reshape.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/reshape.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/tile.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/tile.py) !

 - There are no PEP8 issues in the file [`pandas/core/reshape/util.py`](https://github.com/streeck/pandas/blob/6a2140ecbabf61f7e3605f4610bee02b7b201647/pandas/core/reshape/util.py) !

 @streeck You got error in Travis due to `/pandas/core/reshape/pivot.py:25:1: E303 too many blank lines (3)` . You can locally run flake8 on `pivot.py` to make sure it is in a proper format.  # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23387?src=pr&el=h1) Report
> Merging [#23387](https://codecov.io/gh/pandas-dev/pandas/pull/23387?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/de39bfc5e5c6483cb2669773fa10ddc2e32ca111?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23387/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23387?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23387      +/-   ##
==========================================
- Coverage   92.21%   92.21%   -0.01%     
==========================================
  Files         161      161              
  Lines       51173    51171       -2     
==========================================
- Hits        47190    47188       -2     
  Misses       3983     3983
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.65% <100%> (-0.01%)` | :arrow_down: |
| #single | `42.23% <100%> (-0.01%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23387?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/reshape/pivot.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9waXZvdC5weQ==) | `96.55% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/reshape.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9yZXNoYXBlLnB5) | `99.54% <100%> (-0.01%)` | :arrow_down: |
| [pandas/core/reshape/concat.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9jb25jYXQucHk=) | `97.6% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/util.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS91dGlsLnB5) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/merge.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZXJnZS5weQ==) | `94.01% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/tile.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS90aWxlLnB5) | `94.73% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/api.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9hcGkucHk=) | `100% <100%> (ø)` | :arrow_up: |
| [pandas/core/reshape/melt.py](https://codecov.io/gh/pandas-dev/pandas/pull/23387/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvcmVzaGFwZS9tZWx0LnB5) | `97.32% <100%> (-0.03%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23387?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/23387?src=pr&el=footer). Last update [de39bfc...f5d5b29](https://codecov.io/gh/pandas-dev/pandas/pull/23387?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks for the catch @thoo, made the changes for that file, builds are all green now 😃  can you merge master, we just updated the isort cfg Done 👍  not passing, pls see if you can fix up. Looks like I need to run the sort of imports again for some reason 🤔 
Will do it later today. yes, the isort config changed slightly to reorder some things. pls ping on your open PR's when done. @jreback This one looks like it's good to go again 😃  thanks!