Bump rails_failover.

Bump rails_failover.

diff --git a/Gemfile.lock b/Gemfile.lock
index 6da31e2..1d6cf08 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,6 +1,6 @@
 GIT
   remote: https://github.com/discourse/rails_failover
-  revision: b1a1c4ead35be67d344f092708b540baa0987516
+  revision: 81f5009d7c94f359b7dd0cbca06c327aa95e3851
   specs:
     rails_failover (0.4.0)
       activerecord (~> 6.0)

GitHub sha: 2ffda2b3