DOC: Fix typo of see also in DataFrame stat funcs
fix typo of DataFrame stat functions.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=h1) Report
> Merging [#25388](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/13a505d5541a8fab878c2175f60328f5816b4d25?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/25388/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25388   +/-   ##
=======================================
  Coverage   91.73%   91.73%           
=======================================
  Files         173      173           
  Lines       52841    52841           
=======================================
  Hits        48476    48476           
  Misses       4365     4365
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (ø)` | :arrow_up: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25388/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `94.16% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25388?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/25388?src=pr&el=footer). Last update [13a505d...1ee460e](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=h1) Report
> Merging [#25388](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/13a505d5541a8fab878c2175f60328f5816b4d25?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/25388/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #25388   +/-   ##
=======================================
  Coverage   91.73%   91.73%           
=======================================
  Files         173      173           
  Lines       52841    52841           
=======================================
  Hits        48476    48476           
  Misses       4365     4365
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.3% <ø> (ø)` | :arrow_up: |
| #single | `41.72% <ø> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/25388/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `94.16% <ø> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/25388?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/25388?src=pr&el=footer). Last update [13a505d...1ee460e](https://codecov.io/gh/pandas-dev/pandas/pull/25388?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Thanks @knuu 