don't try to load rubocop in prod

Fix lobsters#599

extras/prohibit_safe_navigation.rb

@@ -1,25 +1,29 @@
-module RuboCop
-  module Cop
-    module Style
-      # The "safe navigation" operator &. makes it easier to work with and
-      # propagate nil values. This will disallow the use of the safe navigation
-      # operator
-      #
-      # @example
-      #
-      #   # bad
-      #   foo&.bar
-      #   a.foo&.bar
-      #
-      class DisallowSafeNavigation < Cop
-        extend TargetRubyVersion
+require "rails"
 
-        MSG = 'Do not use &.'.freeze
+unless Rails.env.production?
+  module RuboCop
+    module Cop
+      module Style
+        # The "safe navigation" operator &. makes it easier to work with and
+        # propagate nil values. This will disallow the use of the safe navigation
+        # operator
+        #
+        # @example
+        #
+        #   # bad
+        #   foo&.bar
+        #   a.foo&.bar
+        #
+        class DisallowSafeNavigation < Cop
+          extend TargetRubyVersion
 
-        minimum_target_ruby_version 2.3
+          MSG = 'Do not use &.'.freeze
 
-        def on_csend(node)
-          add_offense(node)
+          minimum_target_ruby_version 2.3
+
+          def on_csend(node)
+            add_offense(node)
+          end
         end
       end
     end