build_dpkg.sh: fix showing ip address in motd

src/build_dpkg.sh

@@ -131,7 +131,7 @@ cp -R rust/lqos_node_manager/static/* $LQOS_DIR/bin/static
 pushd $MOTD_DIR > /dev/null
 cat <<EOF > 99-libreqos
 #!/bin/bash
-MY_IP=\'hostname -I | cut -d' ' -f1\'
+MY_IP=`hostname -I | cut -d' ' -f1`
 echo -e "\nLibreQoS Traffic Shaper is installed on this machine.
 \nPoint a browser at http://\$MY_IP:9123/ to manage it.\n"
 EOF