to_csv to Google Cloud Storage ignores encoding
#### Code Sample, a copy-pastable example if possible

```python
        df.to_csv(path_or_buf='gs://mybucket/my_file', encoding='utf8')

```
#### Problem description

Instead of expected UTF-8 file is stored in latin-1 on Windows. I can also see that current implementation of method ```pandas.io.gcs.get_filepath_or_buffer``` ignores encoding argument.

I can submit PR if are open to it.

#### Expected Output

Uploaded file encoded in UTF8 even on Windows.

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

<details>

[paste the output of ``pd.show_versions()`` here below this line]
INSTALLED VERSIONS
------------------
commit: None
python: 3.7.1.final.0
python-bits: 64
OS: Linux
OS-release: 4.18.0-17-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.24.2
pytest: None
pip: 10.0.1
setuptools: 39.1.0
Cython: None
numpy: 1.16.2
scipy: None
pyarrow: None
xarray: None
IPython: None
sphinx: None
patsy: None
dateutil: 2.8.0
pytz: 2018.9
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: 0.9.0
pandas_datareader: None
gcsfs: 0.2.1

</details>
