df.hist(sharex=True) does not perform as expected
#### df.hist(sharex=True) does not perform as expected

```python
data = {'Gender':['Female', 'Female', 'Female', 'Male','Female', 'Female', 'Female', 'Male',
                  'Female', 'Female', 'Female', 'Male','Female', 'Female', 'Female', 'Male'], 
        'Degree':['Y','Y','N','N','Y','N','N','Y','Y','Y','N','N','Y','Y','N','N']}
df = pd.DataFrame(data)

df.hist('Degree', by='Gender')

df.hist('Degree', by='Gender', sharex=True)
```
#### Problem description

```df.hist('Degree', by='Gender')```  and ```python df.hist('Degree', by='Gender', sharex=True)```  do not show the same information on their histograms. The x-axis is now shared, after performing sharex=True, but the bars in the histogram do not change, leading to erroneous data interpretation. 

#### Expected Output

When the labels of the x-axis are switched, then the bars plotted in the histogram should follow the labels.

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]



INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Windows
OS-release       : 10
machine          : AMD64
processor        : Intel64 Family 6 Model 69 Stepping 1, GenuineIntel
byteorder        : little
LC_ALL           : None
LANG             : None
LOCALE           : None.None

pandas           : 0.25.3
numpy            : 1.16.5
pytz             : 2019.3
dateutil         : 2.8.0
pip              : 19.2.3
setuptools       : 41.4.0
Cython           : 0.29.13
pytest           : 5.2.1
hypothesis       : None
sphinx           : 2.2.0
blosc            : None
feather          : None
xlsxwriter       : 1.2.1
lxml.etree       : 4.4.1
html5lib         : 1.0.1
pymysql          : None
psycopg2         : None
jinja2           : 2.10.3
IPython          : 7.8.0
pandas_datareader: None
bs4              : 4.8.0
bottleneck       : 1.2.1
fastparquet      : None
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          : None
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : 1.3.9
tables           : 3.5.2
xarray           : None
xlrd             : 1.2.0
xlwt             : 1.3.0
xlsxwriter       : 1.2.1
