work around ruby 2.5 bug

see https://bugs.ruby-lang.org/issues/14273

Change-Id: Id05b2960d782d6c949aeefffa227403e3cce7466
Reviewed-on: https://gerrit.instructure.com/136729
Reviewed-by: James Williams  <jamesw@instructure.com>
Tested-by: Jenkins
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

lib/active_support/cache/ha_store.rb

@@ -56,7 +56,7 @@ class ActiveSupport::Cache::HaStore < ActiveSupport::Cache::RedisStore
           next
         else
           options[:lock_nonce] = lock_nonce
-          return nil
+          break
         end
       end
       entry