BUG: to_json for DataFrame containing Path objects crash with infinite recursion
- [x] I have checked that this issue has not already been reported.

- [x] I have confirmed this bug exists on the latest version of pandas.

- [ ] (optional) I have confirmed this bug exists on the master branch of pandas.

---

When trying to convert a DataFrame that contains Path objects to json it crashes:

```python
import pandas as pd
from pathlib import Path

df = pd.DataFrame({'a': [Path('m1')]})
df.to_json()
```

output

```
Traceback (most recent call last):

  File "<ipython-input-67-05359facf0e6>", line 1, in <module>
    df.to_json()

  File "/home/rikard/.local/lib/python3.7/site-packages/pandas/core/generic.py", line 2305, in to_json
    indent=indent,

  File "/home/rikard/.local/lib/python3.7/site-packages/pandas/io/json/_json.py", line 84, in to_json
    indent=indent,

  File "/home/rikard/.local/lib/python3.7/site-packages/pandas/io/json/_json.py", line 144, in write
    self.indent,

  File "/home/rikard/.local/lib/python3.7/site-packages/pandas/io/json/_json.py", line 244, in _write
    indent,

  File "/home/rikard/.local/lib/python3.7/site-packages/pandas/io/json/_json.py", line 166, in _write
    indent=indent,

OverflowError: Maximum recursion level reached
```

It might be that Path objects are not supported by to_json, but I wouldn't expect an infinite recursion. 


<details>

INSTALLED VERSIONS
------------------
commit           : f2ca0a2665b2d169c97de87b8e778dbed86aea07
python           : 3.7.5.final.0
python-bits      : 64
OS               : Linux
OS-release       : 5.3.0-64-generic
Version          : #58-Ubuntu SMP Fri Jul 10 19:33:51 UTC 2020
machine          : x86_64
processor        : x86_64
byteorder        : little
LC_ALL           : None
LANG             : en_US.UTF-8
LOCALE           : en_US.UTF-8

pandas           : 1.1.1
numpy            : 1.16.2
pytz             : 2019.2
dateutil         : 2.7.3
pip              : 18.1
setuptools       : 41.1.0
Cython           : None
pytest           : 3.7.4
hypothesis       : None
sphinx           : 2.4.4
blosc            : None
feather          : None
xlsxwriter       : None
lxml.etree       : 4.5.0
html5lib         : None
pymysql          : None
psycopg2         : None
jinja2           : 2.11.2
IPython          : 7.10.2
pandas_datareader: None
bs4              : 4.9.0
bottleneck       : None
fsspec           : None
fastparquet      : None
gcsfs            : None
matplotlib       : 3.1.2
numexpr          : None
odfpy            : None
openpyxl         : None
pandas_gbq       : None
pyarrow          : None
pytables         : None
pyxlsb           : None
s3fs             : None
scipy            : 1.1.0
sqlalchemy       : None
tables           : None
tabulate         : None
xarray           : 0.14.1
xlrd             : None
xlwt             : None
numba            : None

</details>
