[Reverted] Use Redis#exists? and fallback to #exists which could be either boolean or integer in recent redis gem versions

lib/vanity/adapters/redis_adapter.rb

@@ -117,7 +117,13 @@ def get_experiment_completed_at(experiment)
 
       def is_experiment_completed?(experiment) # rubocop:todo Naming/PredicateName
         call_redis_with_failover do
-          @experiments.exists("#{experiment}:completed_at")
+          if @experiments.respond_to?(:exists?)
+            @experiments.exists?("#{experiment}:completed_at")
+          else
+            exists = @experiments.exists("#{experiment}:completed_at")
+
+            exists.is_a?(Numeric) ? exists > 0 : exists
+          end
         end
       end
 

test/adapters/redis_adapter_test.rb

@@ -62,7 +62,7 @@ def stub_redis
 
   it "gracefully fails in #is_experiment_completed?" do
     redis_adapter, mocked_redis = stub_redis
-    mocked_redis.stubs(:exists).raises(RuntimeError)
+    mocked_redis.stubs(:exists?).raises(RuntimeError)
 
     assert_silent do
       redis_adapter.is_experiment_completed?("price_options")