fix #745, avoid incompatibility

bin/mailsync

@@ -25,7 +25,7 @@ eval "$(grep -h -- \
 	"$HOME/.profile" "$HOME/.bash_profile" "$HOME/.zprofile"  "$HOME/.config/zsh/.zprofile" "$HOME/.zshenv" \
 	"$HOME/.bashrc" "$HOME/.zshrc" "$HOME/.config/zsh/.zshrc" "$HOME/.pam_environment" 2>/dev/null)"
 
-export GPG_TTY=$TTY
+export GPG_TTY="$(tty)"
 
 [ -n "$MBSYNCRC" ] && alias mbsync="mbsync -c $MBSYNCRC" || MBSYNCRC="$HOME/.mbsyncrc"