add 'Postinstall' stub

Author: Anton-Latukha

scripts/install-nix-from-closure.sh

@@ -807,6 +807,17 @@ installNix() {
     mainInstallNix
 }
 
+}
+
+
+###############################
+###  Postinstall
+###############################
+{
+
+postinstall() {
+}
+
 }
 added=
 if [ -z "$NIX_INSTALLER_NO_MODIFY_PROFILE" ]; then