cannot output csv with IntervalIndex
#### Code Sample, a copy-pastable example if possible

Using `pd.interval_range`:
```python
pd.DataFrame({'a': [1, 2, 3]}, index=pd.interval_range(0, 1, periods=3)).to_csv('hello.csv')
```

Using `pd.IntervalIndex.from_arrays`:
```python
pd.DataFrame({'a': [1, 2, 3]}, index=pd.IntervalIndex.from_arrays(np.array([0, 1, 2]), np.array([1, 2, 3]))).to_csv('hello.csv')
```

#### Problem description

```
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-2-6f913f6c0211> in <module>
----> 1 pd.DataFrame({'a': [1, 2, 3]}, index=pd.IntervalIndex.from_arrays(np.array([0, 1, 2]), np.array([1, 2, 3]))).to_csv('hello.csv')

~/Development/propensity-to-subscribe-modeling/.venv/lib/python3.7/site-packages/pandas/core/generic.py in to_csv(self, path_or_buf, sep, na_rep, float_format, columns, header, index, index_label, mode, encoding, compression, quoting, quotechar, line_terminator, chunksize, date_format, doublequote, escapechar, decimal)
   3226             decimal=decimal,
   3227         )
-> 3228         formatter.save()
   3229 
   3230         if path_or_buf is None:

~/Development/propensity-to-subscribe-modeling/.venv/lib/python3.7/site-packages/pandas/io/formats/csvs.py in save(self)
    200                 self.writer = UnicodeWriter(f, **writer_kwargs)
    201 
--> 202             self._save()
    203 
    204         finally:

~/Development/propensity-to-subscribe-modeling/.venv/lib/python3.7/site-packages/pandas/io/formats/csvs.py in _save(self)
    322                 break
    323 
--> 324             self._save_chunk(start_i, end_i)
    325 
    326     def _save_chunk(self, start_i, end_i):

~/Development/propensity-to-subscribe-modeling/.venv/lib/python3.7/site-packages/pandas/io/formats/csvs.py in _save_chunk(self, start_i, end_i)
    354         )
    355 
--> 356         libwriters.write_csv_rows(self.data, ix, self.nlevels, self.cols, self.writer)

TypeError: Argument 'data_index' has incorrect type (expected numpy.ndarray, got list)
```

#### Expected Output

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

<details>

```
INSTALLED VERSIONS
------------------
commit           : None
python           : 3.7.4.final.0
python-bits      : 64
OS               : Darwin
OS-release       : 18.7.0
machine          : x86_64
processor        : i386
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 0.25.1
numpy            : 1.17.0
pytz             : 2019.2
dateutil         : 2.8.0
pip              : 19.2.2
setuptools       : 41.1.0
Cython           : None
pytest           : None
hypothesis       : None
sphinx           : None
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : None
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.10.1
IPython          : 7.7.0
pandas_datareader: None
bs4              : None
bottleneck       : None
fastparquet      : None
gcsfs            : None
lxml.etree       : None
matplotlib       : 3.1.1
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : 0.14.1
pytables         : None
s3fs             : None
scipy            : 1.3.1
sqlalchemy       : None
tables           : None
xarray           : None
xlrd             : None
xlwt             : None
xlsxwriter       : None
```

</details>
