BUG: in error message raised when invalid axis parameter
#### Code Sample, a copy-pastable example if possible

```python
import numpy as np
from pandas import DataFrame
df = DataFrame(np.random.randn(6, 4))
df.dropna(axis=3)
```
#### Problem description

0.25.0.dev0+198.gd10bbce34
```python-traceback
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\simon\OneDrive\code\pandas-simonjayhawkins\pandas\core\frame.py", line 4575, in dropna
    axis = self._get_axis_number(axis)
  File "C:\Users\simon\OneDrive\code\pandas-simonjayhawkins\pandas\core\generic.py", line 361, in _get_axis_number
    .format(axis, type(cls)))
ValueError: No axis named 3 for object type <class 'type'>
```

0.23.4:
```python-traceback
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-2-5ab8608d1d61> in <module>
      2 from pandas import DataFrame
      3 df = DataFrame(np.random.randn(6, 4))
----> 4 df.dropna(axis=3)

~\Anaconda3\lib\site-packages\pandas\core\frame.py in dropna(self, axis, how, thresh, subset, inplace)
   4274                                        axis=ax)
   4275         else:
-> 4276             axis = self._get_axis_number(axis)
   4277             agg_axis = 1 - axis
   4278 

~\Anaconda3\lib\site-packages\pandas\core\generic.py in _get_axis_number(self, axis)
    373                 pass
    374         raise ValueError('No axis named {0} for object type {1}'
--> 375                          .format(axis, type(self)))
    376 
    377     def _get_axis_name(self, axis):

ValueError: No axis named 3 for object type <class 'pandas.core.frame.DataFrame'>
```
#### Expected Output

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

<details>

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

</details>
