Vim key binding fix: also handle zz binding while selecting text.
Vim key binding fix: also handle zz binding while selecting text.

niklasf/python-prompt-toolkit,ddalex/python-prompt-toolkit,ALSchwalm/python-prompt-toolkit,jaseg/python-prompt-toolkit,amjith/python-prompt-toolkit,jonathanslenders/python-prompt-toolkit,melund/python-prompt-toolkit