This version of babel-loader dropped support for Node < 4. Although 4.2 >= 4, update to 6  for consistency with our other repos, and so that we stay ahead of the curve for any other packages.

Add missing file types to `.gitattributes`.
Use `node` instead of deprecated `stable` version specifier for Travis.
Set dev tool to `cheap-module-source-map`.

Otherwise npm ignores devDependencies

This improves React performance by skipping prop type checks and warnings

Makes local deployment easier

`npm update` does what we want and is less hacky than removing the packages entirely first.  Specify latest as the version so we always get the latest version even though I erroneously installed scratch-blocks@0.1.0.

Once another project uses this package, these should become peerDependencies.  Until then install automatically.

With only one concurrent build, we can't wait for all the jobs to finish first