Promote envify to dependencies and add browserify transform config for it

modules/utils/createRouter.js now contains a `process.env.NODE_ENV` check, which isn't getting envified when react-router gets bundled as a dependency of an app. This change will make that happen.

(You can try `--global-transform` to force envification, but it can get a bit... explodey... if not all your dependencies have envify somewhere in their dependencies)