changing users/view to get instead of post

Hello :)

When trying to use User.view, I get a 405 response form hipchat. The [api documentation](https://www.hipchat.com/docs/apiv2/method/view_user) states that this is a get, so this is one of the changes. 

Another change is to expect a scalar as a result, instead of an array of results. Also, **users_config** is not inside HipChat::ApiVersion::User (and the api version is also not stored there), but in any case, since api v1 is not allowed to use this method, 'v2' is merged in the results. I hope this is ok, it sounds like the minimum viable change to do.

Cheers!