DataFrame.select_dtypes include/exclude "int" not recognized.
#### Code Sample, a copy-pastable example if possible

code sample from DataFrame.select_dtypes docstring

```python
>>> import pandas as pd
>>>
>>> pd.__version__
'0.26.0.dev0+767.gb3490cbd9'
>>>
>>> df = pd.DataFrame({"a": [1, 2] * 3, "b": [True, False] * 3, "c": [1.0, 2.0] * 3})
>>> df
   a      b    c
0  1   True  1.0
1  2  False  2.0
2  1   True  1.0
3  2  False  2.0
4  1   True  1.0
5  2  False  2.0
>>>
>>> df.select_dtypes(exclude=["int"])
   a      b    c
0  1   True  1.0
1  2  False  2.0
2  1   True  1.0
3  2  False  2.0
4  1   True  1.0
5  2  False  2.0
>>>
```
#### Problem description

seen locally on master and 0.25.1

The docstring implies `"int"` is a valid dtype to exclude. Only `"int64"` produces the expected output shown in the docstring.

The same applies to the `include` argument.

#### Expected Output

```python
>>> df.select_dtypes(exclude=["int64"])
       b    c
0   True  1.0
1  False  2.0
2   True  1.0
3  False  2.0
4   True  1.0
5  False  2.0
>>>

```
#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit           : b3490cbd98b96aa5064e87b11c391596e32f7993
python           : 3.7.5.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : Intel64 Family 6 Model 58 Stepping 9, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : en_GB.UTF-8
LOCALE           : None.None

pandas           : 0.26.0.dev0+767.gb3490cbd9
numpy            : 1.17.2
pytz             : 2019.3
dateutil         : 2.8.0
pip              : 19.3.1
setuptools       : 41.6.0.post20191030
Cython           : 0.29.13
pytest           : 5.2.2
hypothesis       : 4.36.2
sphinx           : 2.2.1
blosc            : None
feather          : None
xlsxwriter       : 1.2.2
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.3
IPython          : 7.9.0
pandas_datareader: None
bs4              : 4.8.1
bottleneck       : 1.2.1
fastparquet      : 0.3.2
gcsfs            : None
lxml.etree       : 4.4.1
matplotlib       : 3.1.1
numexpr          : 2.7.0
odfpy            : None
openpyxl         : 3.0.0
pandas_gbq       : None
pyarrow          : 0.15.1
pytables         : None
s3fs             : 0.3.4
scipy            : 1.3.1
sqlalchemy       : 1.3.10
tables           : 3.5.1
xarray           : 0.13.0
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.2
>>>

</details>
