fix indentation in the get_bewit function

As the code is currently written, it's impossible to generate a bewit for a URL unless
that URL has a query string.  This restriction does not exist in the canonical implementation

https://github.com/hueniverse/hawk/blob/7b050d7920c52d1bb4b5ff815c41d60766a2a108/lib/client.js#L229

I have URLs that I wish to generate a bewit for which do not have query strings.  I guess
I could add a bogus ?a=1 query string to the URI, but it looks more likely that the
indentation for this block of code is one level too many.
Awesome, thanks for figuring this out!