.loc[...] = value returns SettingWithCopyWarning 
Code Sample

```python
# My code
df.loc[0, 'column_name'] = 'foo bar'
```
#### Problem description

This code in Pandas 20.3 throws SettingWithCopyWarning and suggests to 

"Try using `.loc[row_indexer,col_indexer] = value` instead".

I am already doing so, looks like there is a little bug. I use Jupyter.
Thank you! :)

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

<details>

------------------
commit: None
python: 3.6.1.final.0
python-bits: 64
OS: Windows
OS-release: 8.1
machine: AMD64
processor: Intel64 Family 6 Model 61 Stepping 4, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None

pandas: 0.20.1
pytest: 3.0.7
pip: 9.0.1
setuptools: 35.0.2
Cython: 0.25.2
numpy: 1.12.1
scipy: 0.19.0
xarray: None
IPython: 5.3.0
sphinx: 1.5.6
patsy: 0.4.1
dateutil: 2.6.0
pytz: 2017.2
blosc: None
bottleneck: 1.2.1
tables: 3.2.2
numexpr: 2.6.2
feather: None
matplotlib: 2.0.2
openpyxl: None
xlrd: 1.0.0
xlwt: 1.2.0
xlsxwriter: 0.9.6
lxml: 3.7.3
bs4: 4.6.0
html5lib: 0.999
sqlalchemy: 1.1.9
pymysql: None
psycopg2: None
jinja2: 2.9.6
s3fs: None
pandas_gbq: None
pandas_datareader: None
</details>
