Fix bytes error in Python 2.7

[aakashns]

Fixes the error:

File "/Users/aakashns/Library/Python/2.7/lib/python/site-packages/jovian/utils/clone.py", line 154, in _sanitize_notebook
    return bytes(json.dumps(nb_content), 'utf-8')
TypeError: str() takes at most 1 argument (2 given)

https://stackoverflow.com/questions/42346984/i-am-getting-this-error-typeerror-str-takes-at-most-1-argument-2-given-at/42347165