Added backslash to quote $ variable substitution in preinst script.

pkg/debian/build.sh

@@ -37,11 +37,7 @@ cat << EOF > "${SERVERROOT}/DEBIAN/preinst"
 
 rm -rf /usr/pgadmin4/venv
 if [ -d /usr/pgadmin4/web ]; then
-  for f in /usr/pgadmin4/web/*; do
-    if [ "${f}" != "/usr/pgadmin4/web/config_local.py" ]; then
-      rm -rf ${f}
-    fi
-  done
+  cd /usr/pgadmin4/web && rm -rf \$(ls -A -I config_local.py)
 fi
 EOF