* Update dependencies
* Use published version of eslint-config-react-app for development
We dogfood on our eslint-config-react-app by using it as our ESLint config,
but installing it from the local folder causes problems when its peerDependencies
are updated, because npm won't update it unless the version number changes.
Use the published version for dogfooding so it can be installed from npm.
* Disable ES2015 transforms based on node version using babel-preset-env
* pass major version number for node to babel-preset-env instead of version string
* use parseFloat() instead of parseInt() to parse node version
* fixed style nits
