Fix C-[ acting as escape

[N0tANick]

I assume the changed line was supposed to let C-[ work as escape to close the window.
That didn't work on my system, so I changed it to use the XKB keysym.

[philj56]

I think this is related to a few past issues (#101, #62, #41), and pretty much boils down to whether the physical key or symbolic sym are used for shortcuts.

I assume you're using a non-qwerty layout? If so, I added an option in 47a7f68 which might be what you need. If you set --physical-keybindings=false, it should honour your keyboard's layout.