v0.26.2

Signing out at a provider could leave someone signed in to Track. Updating a self-hosted copy needs no migration and
no new setting, and the protocol stays at version 25. ([#196])

Fixed

• A provider's logout could be lost. If the provider stopped waiting for the answer, Workers cancelled the
  request and the session stayed, which happened on Gateweave Cloud. A logout that has arrived is now seen through.
  When Track cannot fetch the provider's keys at that moment it answers 503 rather than 400, so that a provider can
  try again, and nothing ends until the token has been checked. ([#196])