Workaround NameError frozen string literal issues with JRuby 9.3 and Rails 5.2/6.0

Author: chadlwilson

src/main/ruby/jruby/rack/helpers.rb

@@ -134,7 +134,7 @@ def resolve_constant(camel_cased_name, context = Object)
             require underscore(camel_cased_name)
             retry
           rescue LoadError => le
-            e.message << " (#{le.message})"
+            e.message = "#{e.message} (#{le.message})"
           end unless required
           raise e
         end