add package-lock=true in .npmrc (go-gitea#9736)

Some users (like me) have this option disabled in their global npm
config which can lead to package-lock.json not being updated. This
explicitely enables the option for this repo, so that the file is
always updated when adding/removing dependencies.

Co-authored-by: techknowlogick <matti@mdranta.net>
Co-authored-by: Antoine GIRARD <sapk@users.noreply.github.com>

.npmrc

@@ -1 +1,2 @@
+package-lock=true
 save-exact=true