Make sandbox/validator.html work in Chrome

Fixes #112 

The validator makes use of `toSource`: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/toSource which is a non-standard method that only works in Firefox. The code that makes use of `toSource` seems to be dead, therefore I'm pretty sure that we can just remove the lines. I tested the changed code in Chrome and Firefox and works.