fillna ignoring axis=1 parameter
#### Code Sample, a copy-pastable example if possible

```
df = pd.DataFrame({'Col1':[np.nan]*5,
                   'Col2':[1]*5,
                   'Col3':[2,np.nan,2,2,2],
                   'Col4':[3,np.nan,3,np.nan,3],
                   'Col5':[4,np.nan,np.nan,np.nan,4],
                   'Col6':[np.nan]*5,
                   'Col7':[np.nan]*5,
                   'Col8':[np.nan]*5})

print(df)

   Col1  Col2  Col3  Col4  Col5  Col6  Col7  Col8
0   NaN     1   2.0   3.0   4.0   NaN   NaN   NaN
1   NaN     1   NaN   NaN   NaN   NaN   NaN   NaN
2   NaN     1   2.0   3.0   NaN   NaN   NaN   NaN
3   NaN     1   2.0   NaN   NaN   NaN   NaN   NaN
4   NaN     1   2.0   3.0   4.0   NaN   NaN   NaN

df.fillna(0,limit=2,axis=1)


   Col1  Col2  Col3  Col4  Col5  Col6  Col7  Col8
0   0.0     1   2.0   3.0   4.0   0.0   0.0   0.0
1   0.0     1   0.0   0.0   0.0   0.0   0.0   0.0
2   NaN     1   2.0   3.0   0.0   NaN   NaN   NaN
3   NaN     1   2.0   0.0   NaN   NaN   NaN   NaN
4   NaN     1   2.0   3.0   4.0   NaN   NaN   NaN
```


#### Problem description

df.fillna is ignoring axis=1 parameter


#### Expected Output
`df.T.fillna(0,limit=2,axis=1).T`

```
   Col1  Col2  Col3  Col4  Col5  Col6  Col7  Col8
0   0.0   1.0   2.0   3.0   4.0   0.0   NaN   NaN
1   0.0   1.0   0.0   NaN   NaN   NaN   NaN   NaN
2   0.0   1.0   2.0   3.0   0.0   NaN   NaN   NaN
3   0.0   1.0   2.0   0.0   NaN   NaN   NaN   NaN
4   0.0   1.0   2.0   3.0   4.0   0.0   NaN   NaN
```


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

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 26 Stepping 5, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.20.3
pytest: 2.9.2
pip: 9.0.1
setuptools: 27.2.0
Cython: 0.25.2
numpy: 1.13.1
scipy: 0.19.0
xarray: 0.9.6
IPython: 5.1.0
sphinx: 1.4.6
patsy: 0.4.1
dateutil: 2.6.1
pytz: 2017.2
blosc: None
bottleneck: 1.1.0
tables: 3.2.2
numexpr: 2.6.2
feather: None
matplotlib: 2.0.0
openpyxl: 2.3.2
xlrd: 1.0.0
xlwt: 1.1.2
xlsxwriter: 0.9.3
lxml: 3.6.4
bs4: 4.5.1
html5lib: 0.999999999
sqlalchemy: 1.0.13
pymysql: None
psycopg2: None
jinja2: 2.8
s3fs: None
pandas_gbq: None
pandas_datareader: 0.2.1

