Update es5-sham.js

once again, Opera Mini supports `__proto__` but not `Object.getPrototypeOf` which means how it was would easily fall into infinite recursion.

As extra note, I would recommend to put your tests online so you can directly verify in there.
Jasmine locally is not a good option since Opera Mini as other server side based browsers will not be able to access your intranet.

Best Regards