brave: add update script

The Brave package often seems to get very outdated. This is bad for a
browser, where vulnerabilities are high impact.

This change adds an update script, so that r-ryantm will suggest
updates. We find the latest version using their Debian package
database (since we are using the Debian package anyway).

pkgs/applications/networking/browsers/brave/update.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env nix-shell
+#!nix-shell -i bash -p curl gnused common-updater-scripts
+
+version="$(curl -sL https://brave-browser-apt-release.s3.brave.com/dists/stable/main/binary-amd64/Packages | sed -r -n 's/^Version: (.*)/\1/p' | head -n1)"
+update-source-version brave "$version"