BLD: 3.6.1 ABI compat
 - [x] closes #15961
 - [ ] tests added / passed
 - [ ] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [ ] whatsnew entry

So I _think_ this works - locally was able to build a wheel with `3.6.1` and import it into a `3.6.0` environment, which was failing before this patch.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=h1) Report
> Merging [#16066](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b17e28638995bbfc32bc3dd7c53cd8a343191e58?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16066/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&height=150&width=650)](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16066      +/-   ##
==========================================
- Coverage   90.84%   90.82%   -0.03%     
==========================================
  Files         159      159              
  Lines       50791    50791              
==========================================
- Hits        46143    46131      -12     
- Misses       4648     4660      +12
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.6% <ø> (-0.03%)` | :arrow_down: |
| #single | `40.36% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/plotting/\_converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=tree#diff-cGFuZGFzL3Bsb3R0aW5nL19jb252ZXJ0ZXIucHk=) | `63.54% <0%> (-1.82%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16066?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/16066?src=pr&el=footer). Last update [b17e286...f082210](https://codecov.io/gh/pandas-dev/pandas/pull/16066?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks @chris-b1 @njsmith 