Update Nginx test

The `server-configs-nginx` project recentlly renamed the `conf`
directory to `h5bp`.

Ref: https://github.com/h5bp/server-configs-nginx/commit/e476b08d115d1834e8196fdd31fe29791e04535b.
Make generator work with `yo` v1.0.5

* Update `peerDependencies` and `dependencies`.
* Change generator to inherit from the base Yeoman generator.
v0.2.1