fix: [installer] Fix a bug where the installer fails if apt update has never been run

docs/generic/supportFunctions.md

@@ -229,6 +229,7 @@ checkInstaller () {
   else
     # TODO: Implement $FLAVOUR checks and install depending on the platform we are on
     if [[ $(which shasum > /dev/null 2>&1 ; echo $?) != 0 ]]; then
+      sudo apt update
       sudo apt install libdigest-sha-perl -qyy
     fi
     # SHAsums to be computed, not the -- notatiation is for ease of use with rhash