warning: ObjectSpace impacts performance

~~Currently it does not work with latest Burp.~~

My bad, should have used `jruby-complete.jar` instead of `jruby.jar`. It loads with following warning:

```text
/lib/buby/burp_extender/console_pane.rb:22: warning: ObjectSpace impacts performance. See http://wiki.jruby.org/PerformanceTuning#dont-enable-objectspace
```