fix private constant as rubocop warns

Author: danmayer

lib/dalli/protocol/base.rb

@@ -152,9 +152,10 @@ def quiet?
 
       # NOTE: Additional public methods should be overridden in Dalli::Threadsafe
 
+      ALLOWED_QUIET_OPS = %i[add replace set delete incr decr append prepend flush noop].freeze
+
       private
 
-      ALLOWED_QUIET_OPS = %i[add replace set delete incr decr append prepend flush noop].freeze
       def verify_allowed_quiet!(opkey)
         return if ALLOWED_QUIET_OPS.include?(opkey)