commit fcd4e9d

app: treat Shift+Backspace as Backspace

before ffb806d777cb0123d276f0c03463fa0fdda1a4ae, both Shift+Backspace
and Ctrl+Backspace acted as "erase previous character", but since then
Backspace does nothing if modified by Shift or Ctrl. I find that I often
try to backspace while still having Shift held down from a previous
character I typed, so make Shift+Backspace work as it did previously.

 1@@ -747,6 +747,10 @@ func (app *App) handleKeyEvent(ev vaxis.Key) {
 2 		if app.win.InputBackspace() {
 3 			app.typing()
 4 		}
 5+	} else if keyMatches(ev, vaxis.KeyBackspace, vaxis.ModShift) {
 6+		if app.win.InputBackspace() {
 7+			app.typing()
 8+		}
 9 	} else if keyMatches(ev, vaxis.KeyDelete, 0) {
10 		if app.win.InputDelete() {
11 			app.typing()