Fix typo in sequel.rb

Author: codeconscious

lib/flipper/adapters/sequel.rb

@@ -30,7 +30,7 @@ class Gate < ::Sequel::Model(:flipper_gates)
       end
 
       VALUE_TO_TEXT_WARNING = <<-EOS
-        Your database needs migrated to use the latest Flipper features.
+        Your database needs to be migrated to use the latest Flipper features.
         See https://github.com/flippercloud/flipper/issues/557
       EOS