Change in python behaviour

Since python 3.7, the sys.path behaviour changed:
https://docs.python.org/3/whatsnew/3.7.html#changes-in-python-behavior

> When using the -m switch, the initial working directory is now added to sys.path, rather than an empty string (which dynamically denoted the current working directory at the time of each import). Any programs that are checking for the empty string, or otherwise relying on the previous behaviour, will need to be updated accordingly (e.g. by also checking for os.getcwd() or os.path.dirname(__main__.__file__), depending on why the code was checking for the empty string in the first place).

I don't know if ipykernel should be updated (see https://github.com/ipython/ipykernel/blob/9181966528c79d9f67e565e85d12439ec95a43bf/ipykernel_launcher.py#L12)

For reference: https://github.com/spyder-ide/spyder-kernels/pull/222