nixos/doc: include extensions in postgresql upgrade script

nixos/modules/services/databases/postgresql.md

@@ -207,15 +207,15 @@ For an upgrade, a script like this can be used to simplify the process:
       export NEWBIN="${newPostgres}/bin"
 
       export OLDDATA="${cfg.dataDir}"
-      export OLDBIN="${cfg.package}/bin"
+      export OLDBIN="${cfg.finalPackage}/bin"
 
       install -d -m 0700 -o postgres -g postgres "$NEWDATA"
       cd "$NEWDATA"
-      sudo -u postgres $NEWBIN/initdb -D "$NEWDATA" ${lib.escapeShellArgs cfg.initdbArgs}
+      sudo -u postgres "$NEWBIN/initdb" -D "$NEWDATA" ${lib.escapeShellArgs cfg.initdbArgs}
 
-      sudo -u postgres $NEWBIN/pg_upgrade \
+      sudo -u postgres "$NEWBIN/pg_upgrade" \
         --old-datadir "$OLDDATA" --new-datadir "$NEWDATA" \
-        --old-bindir $OLDBIN --new-bindir $NEWBIN \
+        --old-bindir "$OLDBIN" --new-bindir "$NEWBIN" \
         "$@"
     '')
   ];