Failing tests due to change in matplotlib behaviour in 3.1.0
The allowed failures on Travis is currently failing on TestDataFramePlots.test_subplots

the matplotlib version used has changed today from 3.0.3 to 3.1.0

#### Code Sample, a copy-pastable example if possible

```python
import matplotlib
print(matplotlib.__version__)
import numpy as np
import string
from pandas import DataFrame
df = DataFrame(np.random.rand(10, 3),
               index=list(string.ascii_letters[:10]))

axes = df.plot(kind='bar', subplots=True, sharex=True, legend=True)
for ax in axes[:-2]:
    collections = ax.get_xticklabels(minor=True)
    print(collections)
    for patch in collections:
        print(patch.get_visible())
```
#### Problem description

3.1.0
<a list of 2 Text xticklabel objects>
True
True

#### Expected Output

3.0.3
<a list of 7 Text xticklabel objects>
False
False
False
False
False
False
False
#### Output of ``pd.show_versions()``

<details>

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

</details>
