Upgrade vis.js Version

[jrtechs]

Since vis.js split apart into smaller communities a few months ago, we should update the version that we are currently using. This will make it easier to upgrade to newer versions in the future. Due to the split, we will have to update the timeline and network components separately moving into the future.

We are currently using vis.js version 4.20.0 which was published in May of 2017.

The current version is 6.5.0
https://github.com/visjs/vis-timeline
https://github.com/visjs/vis-network

This should just be a matter of updating the files in:
https://github.com/jrtechs/github-graphs/tree/master/public/js/vis
however, we will have to do some testing to make sure that nothing broke before we push to production.