Pr unicode encode error

[xarx00]

This fixes the exception

Traceback (most recent call last):
  File "c:\program files\python37\lib\site-packages\gitlab\v4\bulk.py", line 429, in clone
    git.Repo.clone_from(url, wdpath)
  File "c:\program files\python37\lib\site-packages\git\repo\base.py", line 988, in clone_from
    return cls._clone(git, url, to_path, GitCmdObjectDB, progress, **kwargs)
  File "c:\program files\python37\lib\site-packages\git\repo\base.py", line 939, in _clone
    finalize_process(proc, stderr=stderr)
  File "c:\program files\python37\lib\site-packages\git\util.py", line 333, in finalize_process
    proc.wait(**kwargs)
  File "c:\program files\python37\lib\site-packages\git\cmd.py", line 402, in wait
    stderr = force_bytes(stderr)
  File "c:\program files\python37\lib\site-packages\gitdb\utils\encoding.py", line 16, in force_bytes
    return data.encode(encoding)
UnicodeEncodeError: 'ascii' codec can't encode characters in position 29-32: ordinal not in range(128)

in git.repo.clone_from(url, path) when path contains non-ascii characters.
The stderr string being encoded contains

Cloning into 'W:\SBER\Repozitář\test/test1'...
POST git-upload-pack (237 bytes)

Very probably, this error can occur in other situations too, hence I changed the default encoding here, into the gitdb utils.

Edit: This PR is related to gitpython-developers/GitPython#761 and #48.