Pass URI to socket.io-client to specify namespace

[jimklo]

The example app-namespace.py which uses templates/index.html
did not correctly initialize the socket.io-client with the /test
namespace. This prevented the client from communicating with
the example application.

This modification, constructs the URI based upon the current
window.location, and apppends /test so the client subscribes
to the correct namespace.

[miguelgrinberg]

This was a mistake on my part. At some point I simplified the app.py example to use the default namespace, and forgot that both app.py and app_namespace.py share the same index.html. The correct fix here is not in the html file, we want app_namespace.py to use the / namespace instead of /test, and that way both examples will work.