Update browserify to 4.2.0, which renames internal require.

This updates browserify to 4.2.x, which brings uses [derequire](https://github.com/calvinmetcalf/derequire) when using the `--standalone` option. Using `require` inside a standalone build usually throws off AMD loaders like Require.js.

The tests continue to pass and the only diff in the build is replacing internal `require`s with `_dereq_`.