Supress Powershell popping up in pyinstaller .exe

[dynobo]

Hi, I noticed a bug of notify-py in combination with PyInstaller on Windows (10):
If a program using notify-py is compiled to an .exe with the --windowed flag, the powershell windows pop's up for second when a notification is shown.

This commit should fix it.

To reproduce:

1. Deps:

   pip install pyinstaller notify-py

2. Create test.py:

   from notifypy import Notify
   notification = Notify()
   notification.send(block=False)

3. Compile to .exe:

   pyinstaller --windowed test.py

4. Run ./dist/test/test.exe

Result:

[dynobo]

Uh, black throws error on files I didn't touch:

[...]
would reformat /home/runner/work/notify-py/notify-py/notifypy/cli.py
would reformat /home/runner/work/notify-py/notify-py/notifypy/notify.py

Shall I reformat and commit again?

[ms7m]

Don't worry about that, I'll handle it.
Thanks for PR!