D3 4 Upgrade

This release upgrades dependencies to the D3 v4 modules. Many thanks to @Hypercubed for upgrading via #8 .

The breaking changes here relate to the new D3 time interval names (as an example, see https://github.com/curran/data-reduction/pull/8/files#diff-1dd241c4cd3fd1dd89c570cee98b79ddL271).