Support for recent version of JavaScript

[HoLyVieR]

This project doesn't seems to be maintained anymore, so I'm leaving this as an issue instead of a PR. For anyone that's looking to do parsing with JavaScript file that esprima can't parse (ex.: with newer features & syntax), I did a fork that switched the AST engine to acorn and fixed some of the analysis issue that's encountered with recent features. It should work on most recently written file, but there may be some issues here and there.

Fork : https://github.com/holyvier/js-callgraph

[HoLyVieR]

I should note that the fork is a potential fix for #54, #67 and #46 . Referencing here if people are looking for solution to those issues.