Update core.js

BugFix
Expression this && this[0] && this[0].nodeType may lead to SecurityException in following case:
1) we use baron as standalone function, so this === window
2) window contains iframe from another domain (disqus widget will be nice example), so this[0] == window[0] - is disqus window, which is in another domain
3) this[0].nodeType will lead to SecurityException
Merge pull request #51 from mialinx/master

Update core.js