Inappropriate use of  for-in loop in bibtexParser.toBibtex()

In toBibtex() a for-in loop is used to iterate over the array, which is inappropriate as this includes the object's properties if any are set. I've change the function to use .forEach() which will only iterate the array elements. I also added a basic test to demonstrate the problem.

I ran into this using the library in emberjs where properties are assigned the array object that were then iterated over.