Add non-free for security repo, and add sudo command for sed

scripts/install

@@ -79,9 +79,9 @@ export DEBIAN_FRONTEND=noninteractive
 if [ "${firmware_nonfree}" == yes ]; then
   # check if non-free is set on sources.list
   if ! grep -q non-free /etc/apt/sources.list ; then
-    sed -i -e '0,/main/{s/main/main non-free/}' /etc/apt/sources.list
-    apt-get update
+    sudo sed '/debian/{s/main/& non-free/}' -i /etc/apt/sources.list
   fi
+
   packages="$packages firmware-atheros atmel-firmware firmware-linux-free firmware-linux-nonfree firmware-realtek firmware-ralink firmware-libertas zd1211-firmware"
 else
   packages="$packages firmware-linux-free"