Adding miniscore replacement for Object.keys for IE8 & Safari < 5 support

per @bermi https://github.com/bermi/eventify/commit/ea6e78ef61758e2dbbad109db041be712e2a76af#diff-a9aa7770fdb99bfd751dd94457b4b0f5L33

Addresses https://github.com/n1k0/backbone-events-standalone/issues/6 and relatedly https://github.com/openannotation/annotator/issues/408#issuecomment-51883990