Unable to insert datetime object

**Environment info**
Operating System: Windows 10
Python version: 2.7.12
gspread version: 2.0.0

**Steps to reproduce**
1. worksheet.insert_row([datetime.datetime.now()])

Traceback:
```
Traceback (most recent call last):
File "D:/gspreadinserttest.py", line 21, in
sh.insert_row([datetime.datetime.now()])
File "C:\Python27\lib\site-packages\gspread\v4\models.py", line 685, in insert_row
'values': [values]
File "C:\Python27\lib\site-packages\gspread\v4\models.py", line 112, in values_update
r = self.client.request('put', url, params=params, json=body)
File "C:\Python27\lib\site-packages\gspread\v4\client.py", line 67, in request
endpoint, json=json, params=params, data=data, files=files
File "C:\Python27\lib\site-packages\requests\sessions.py", line 566, in put
return self.request('PUT', url, data=data, **kwargs)
File "C:\Python27\lib\site-packages\requests\sessions.py", line 494, in request
prep = self.prepare_request(req)
File "C:\Python27\lib\site-packages\requests\sessions.py", line 437, in prepare_request
hooks=merge_hooks(request.hooks, self.hooks),
File "C:\Python27\lib\site-packages\requests\models.py", line 308, in prepare
self.prepare_body(data, files, json)
File "C:\Python27\lib\site-packages\requests\models.py", line 458, in prepare_body
body = complexjson.dumps(json)
File "C:\Python27\lib\json\__init__.py", line 231, in dumps
return _default_encoder.encode(obj)
File "C:\Python27\lib\json\encoder.py", line 201, in encode
chunks = self.iterencode(o, _one_shot=True)
File "C:\Python27\lib\json\encoder.py", line 264, in iterencode
return _iterencode(o, 0)
File "C:\Python27\lib\json\encoder.py", line 178, in default
raise TypeError(repr(o) + " is not JSON serializable")
TypeError: datetime.datetime(2018, 3, 11, 13, 26, 34, 292000) is not JSON serializable
```

I know it is possible to convert to a string before inserting however in previous gspread versions I could insert a datetime object and it would format the datetime using the formatting from the google sheet. Is there anyway this kind of functionality could be replicated in 2.0.0?