fix mixed function name

opensearch-1.x-node-installer.sh

@@ -30,7 +30,7 @@ NL="$(printf '\n  ')"
 printwc() {
     printf "%b$2%b" "$1" "${Color_Off}"
 }
-install_ifnot() {
+install_if_not() {
     if [ "$(dpkg-query -W -f='${Status}' "$1" 2>/dev/null | \
         grep -c "ok installed")" == "1" ]; then
         echo " $1 is installed, skipping..."