d/ostree-boot.postinst: Trigger an update of the initramfs

Otherwise the dracut initramfs won't be rebuilt to include ostree-boot.

debian/ostree-boot.postinst

@@ -0,0 +1,11 @@
+#!/bin/sh
+
+set -e
+
+case "$1" in
+    (configure)
+        dpkg-trigger --no-await update-initramfs
+        ;;
+esac
+
+#DEBHELPER#