Live Demo build fix: Update to react-scripts 2.x.x

[4lgn]

Issue: Live Demo GitHub Pages, linked from the README, does not work and simply gives users a blank page with a deprecated API notice (#28).

The actual code, if run locally, works fine, so it seems that the gh-pages branch which deploys the Live Demo is simply using an old build which depends on the deprecated web3 window object injection.

This PR simply updates react-scripts to version 2 from version 1 to fix some code minification errors during build, and allows to deploy the Live Demo with the updated code by running deploy script.

@danfinlay I can see you have made all the commits to the gh-pages branch. If this was done by manually building and committing up to that branch, do you want me to create a new build and make a PR for the other branch as well? Let me know.