Fix description of autoload spec

Author: eregon

spec/ruby/core/kernel/autoload_spec.rb

@@ -57,7 +57,7 @@ def check_autoload(const)
   end
 
   describe "when Object is frozen" do
-    it "raises a FrozenError before defining the constant" do
+    it "raises a #{frozen_error_class} before defining the constant" do
       ruby_exe(fixture(__FILE__, "autoload_frozen.rb")).should == "#{frozen_error_class} - nil"
     end
   end