Fix warning message from name clashing

Hi,

I'm using your google oauth script for a project realized in collaboration with @jfiger.
During each authentification, apache errors.log shows me the current error :
```
Prototype mismatch: sub GoogleOauth::oauth::url ($;$) vs none at /usr/share/perl/5.18/CGI.pm line 308.
```
After investigation, I figured this is due to a name clash between modules (see pretty similar error related on this thread http://www.perlmonks.org/?node_id=986481)