Fix JS exception in IE due to router inheritance

This should fix #121. In IE, there was a JS error thrown by the
`BaseRouter`'s constructor. It turns out it's just an issue with the way
the example app sets up prototypical inheritance -- IE doesn't support
setting `Router.prototype.__proto__ = BaseClientRouter.prototype`, so we
use `Object.create()` instead, which works in IE due to the polyfill
provided by `es5shim`/`es5sham`.

This same change was made for `airbnb/rendr-app-template` 21 days ago (https://github.com/airbnb/rendr-app-template/commit/cfee163a1c873758e7b148a3629d035031b47399) however it never made in into the examples in this repo.