Fix a bug where the wrong path was being signed

If you have set a baseURL which is something like: http://api.something.com/1/
When you do the following:

```objective-c
[self requestWithMethod:@"GET" path:@"user" parameters:nil];
```

The URL should be:

    http://api.something.com/1/user

Thus, the path should be:

    /1/user

However, it is passing the suffix of the path to the oauth signing code so it
is instead signing:

    user