Correct signature for openid based strategy in Google example

The Google strategy is based on OpenID.  In this case, the verify callback gets called with the profile as the second argument (if the arity is > 2).  The `accessToken` and `refreshToken` args are relevant for OAuth based strategies.

In the case where you provide [four args](https://github.com/jaredhanson/passport-openid/blob/v0.3.1/lib/passport-openid/strategy.js#L214), the callback is called with `(identifier, profile, pape, verified)`.  Since the `pape` isn't used here, I think the example is simpler with just 3 args.