Support sub-directory without file name

Hi. I added the supported URL.

Currently  `http://localhost:3000/` works fine,
but sub-directory, such as `http://localhost:3000/foo/` or `http://localhost:3000/foo/?params` isn't supported.
I fixed this issue.

And I have another improvement related to the "browser-sync-client.js".
I will send one more PR later.