preserve hooks

lib/self-upgrade.bash

@@ -50,6 +50,7 @@ function perform_upgrade {
   local backup="$MIAOU_BASH_DIR".before_upgrade
   sudo mv "$MIAOU_BASH_DIR" "$backup"
   if "$backup"/install.sh upgraded; then
+    sudo mv "$backup"/hooks.d/* "$MIAOU_BASH_DIR/hooks.d/"
     sudo rm -rf "$backup"
     cat <<EOF
 To reset this session, you can run: