CI: Allow to compile docs with ipython 7.11 #22990
- [ ] closes #22990 
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry
Hello @benoxoft! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`doc/source/conf.py`](https://github.com/benoxoft/pandas/blob/62dd43b1a5351f055f5e6e2c94adfbb6a7944cc3/doc/source/conf.py) !

 Thanks. We'll want to check the output of `show environment` in https://travis-ci.org/pandas-dev/pandas/jobs/454181367 once it runs, to make sure IPython 7.1.1 was installed. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23655?src=pr&el=h1) Report
> Merging [#23655](https://codecov.io/gh/pandas-dev/pandas/pull/23655?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a08bf3de02bb1e53fb95df24ae060b63c2a44c96?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23655/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23655?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23655   +/-   ##
=======================================
  Coverage   92.24%   92.24%           
=======================================
  Files         161      161           
  Lines       51317    51317           
=======================================
  Hits        47338    47338           
  Misses       3979     3979
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.63% <ø> (ø)` | :arrow_up: |
| #single | `42.31% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23655?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/23655?src=pr&el=footer). Last update [a08bf3d...62dd43b](https://codecov.io/gh/pandas-dev/pandas/pull/23655?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 @TomAugspurger I checked the output of the job 46992.7 which should be the job for the documentation and I found this at line #1445:
```
ipython                   7.1.1            py36h39e3cac_0  
```

Link: https://travis-ci.org/pandas-dev/pandas/jobs/454181367#L1445
 Perfect, thanks for checking!