ruby: better configuration assert message

src/mem/ruby/config/cfg.rb

@@ -11,7 +11,7 @@ end
 
 def assert(condition,message)
   unless condition
-    raise AssertionFailure, "Assertion failed: #{message}"
+    raise AssertionFailure, "\n\nAssertion failed: \n\n   #{message}\n\n"
   end
 end