Add clarification about JRuby 9.1 workaround

Author: pirj

lib/rspec/mocks/test_double.rb

@@ -84,13 +84,16 @@ def method_missing(message, *args, &block)
           end
         end
 
+        visibility = proxy.visibility_for(message)
+
         # Defined private and protected methods will still trigger `method_missing`
         # when called publicly. We want ruby's method visibility error to get raised,
         # so we simply delegate to `super` in that case.
+        #   return super if visibility == :private || visibility == :protected
         # ...well, we would delegate to `super`, but there's a JRuby
         # bug, so we raise our own visibility error instead:
         # https://github.com/jruby/jruby/issues/1398
-        visibility = proxy.visibility_for(message)
+        # Only works without this workaround with JRuby 9.2
         if visibility == :private || visibility == :protected
           ErrorGenerator.new(self).raise_non_public_error(
             message, visibility