Update `rails_failover`.

Update rails_failover.

diff --git a/Gemfile.lock b/Gemfile.lock
index 12eb274..53a0a69 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,6 +1,6 @@
 GIT
   remote: https://github.com/discourse/rails_failover
-  revision: 0e668eba86591c20aa7a43f47b0cd36d4eacaeb6
+  revision: 291bf1c18e9a704556a40204d8160549d0438e96
   specs:
     rails_failover (0.4.0)
       activerecord (~> 6.0)

GitHub sha: deb84017