fix bug #150.
fix #150, edge weight 0 turns false, now use /\d/.test() to check if it is a number first.
clean console.log
if you want get path to the vertex is the start vertex, you will get an empty array.
Merge branch 'master' of https://github.com/liwenzhu/natural into liwenzhu-master
added unit test for #150
Merge branch 'master' of github.com:NaturalNode/natural