Use Ctrl-Down as close editor shortcut

[estan]

@marijnh Going through your great book (thanks!).

This PR changes to Ctrl-' Ctrl-Down instead of Ctrl-` as the keyboard shortcut for leaving the editor in the examples, since many non-US keyboards do not have a backtick key, making it's impossible to enter the shortcut. For example my Swedish keyboard has none, and the only way to enter a backtick is as a diacritic for space (Shift-' followed by Space).

Hope that's OK. Let me know if another shortcut is more appropriate.

[marijnh]

Oh, right, that's awkward. Would Ctrl-Down also work for you? That's probably easier to read and understand.

[estan]

@marijnh Good idea, changed to Ctrl-Down (yes I do have a Down key :) )

[marijnh]

Thanks! Merged.

[estan]

@marijnh BTW how often do you update the copy at http://eloquentjavascript.net/ ? I could use this advanced Ctrl-Down functionality right about now :)

[marijnh]

Should be updated now!