BUG: fix missing sort keyword for PeriodIndex.join
 - [x] closes #16541
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master --name-only -- '*.py' | flake8 --diff``
 - [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=h1) Report
> Merging [#16586](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8d197ba63128a4cdbbb8627e48e7f1b4f150330c?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/16586/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #16586      +/-   ##
==========================================
- Coverage   90.99%   90.97%   -0.02%     
==========================================
  Files         161      161              
  Lines       49283    49291       +8     
==========================================
- Hits        44843    44842       -1     
- Misses       4440     4449       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.74% <100%> (ø)` | :arrow_up: |
| #single | `40.16% <66.66%> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/indexes/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy90aW1lZGVsdGFzLnB5) | `90.58% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9iYXNlLnB5) | `95.8% <100%> (ø)` | :arrow_up: |
| [pandas/core/indexes/period.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9wZXJpb2QucHk=) | `92.74% <100%> (ø)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.71% <0%> (-0.1%)` | :arrow_down: |
| [pandas/core/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhlcy9tdWx0aS5weQ==) | `96.66% <0%> (+0.01%)` | :arrow_up: |
| [pandas/compat/numpy/function.py](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=tree#diff-cGFuZGFzL2NvbXBhdC9udW1weS9mdW5jdGlvbi5weQ==) | `93.12% <0%> (+0.17%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/16586?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/16586?src=pr&el=footer). Last update [8d197ba...2aea2b5](https://codecov.io/gh/pandas-dev/pandas/pull/16586?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 added the note.  looks like the circleci failed on a conda HTTP timeout.  can someone kick off again (i don't have privileges). All good here? @jreback  This is a regression, so should target 0.20.3

@erbian Can you move the whatsnew notice to the 0.20.3 file ? pls ``git  rebase -i upstream/master`` then ``git push yourbrachname yourfork -f``

 breaking on bug in `numpy 1.13.0 + python 3.6` where `np.array.sort` no longer handles int + str arrays (Issue here: https://github.com/numpy/numpy/issues/9236).  That method is called in `np.unique` @erbian Do you have time to update this? (would be nice to get this into 0.20.3, due for next week) Fairly busy with other things. I can try to get to it over the weekend.

On Jun 29, 2017 8:28 AM, "Joris Van den Bossche" <notifications@github.com>
wrote:

> @erbian <https://github.com/erbian> Do you have time to update this?
> (would be nice to get this into 0.20.3, due for next week)
>
> —
> You are receiving this because you were mentioned.
> Reply to this email directly, view it on GitHub
> <https://github.com/pandas-dev/pandas/pull/16586#issuecomment-311951594>,
> or mute the thread
> <https://github.com/notifications/unsubscribe-auth/AKKj3-4Ner9uYsyXP-ekmsQncK7Cg5oFks5sI5htgaJpZM4Nutqj>
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>
 @jorisvandenbossche are we good here? @erbian can you edit for comments. releasing 0.20.3 tomorrow and want to push this in. ok @jreback @jorisvandenbossche I edited for latest comments and cleaned up the PR (4 commits now).  It is rebased on latest upstream/master as well.
 @TomAugspurger I think this is the last PR for 0.20.3. waiting on pass to merge. Cool. Looks like it's next in line for Appveyor. I'll merge it on green and start the release stuff. thanks @erbian 