api: improve old-os checking

api

@@ -402,8 +402,8 @@ is_supported_system() {
   if uname -m | grep -q 'x86' || uname -m | grep -q 'i686' || uname -m | grep -q 'i386';then
     echo "Pi-Apps is not supported on x86 processors. Expect almost all apps to fail. Consider switching to this x86 port of Pi-Apps: https://github.com/MCRaspRBX/pi-apps-x86"
     return 1
-  elif [[ "$(cat /etc/os-release | grep VERSION_CODENAME | tr -d '"' | awk -F= '{print $2}' | tr '[A-Z]' '[a-z]')" == @(stretch|wheezy|jessie) ]];then
-    echo "Pi-Apps is not supported on the outdated $(cat /etc/os-release | grep VERSION_CODENAME | tr -d '"' | awk -F= '{print $2}') operating system. Expect many apps to fail. Consider upgrading your operating system."
+  elif cat /etc/os-release | grep PRETTY_NAME | tr -d '"' | awk -F= '{print $2}' | grep -qi 'stretch\|wheezy\|jessie';then
+    echo "Pi-Apps is not supported on your outdated operating system. Expect many apps to fail. Consider upgrading your operating system."
     return 1
   elif [[ "$(uname -m)" == armv6* ]];then
     echo "Pi-Apps has not been tested on armv6 Raspberry Pi boards. Expect many apps to fail."