Touch taxonomy when taxon is created/updated.

There is a cache within this block:
https://github.com/spree/spree/blob/7ff3bcc81af3a421ed0013511c6ee3049fb240c2/frontend/app/views/spree/shared/_taxonomies.html.erb#L4-L7

This cache needs to be invalidated so that the taxons_tree can be drawn
properly. Currently, new taxons, or modified taxons will not show up
until the Taxonomy is updated, or the cache is cleared.

Fixes #5810