Cannot access fetcherAuthorizer property on GIDAuthentication from swift

[lilpit]

The fetcherAuthorizer method signature is not visible in swift generated interface of GIDAuthentication .
This prevent the use of this library to work with https://github.com/google/google-api-objectivec-client-for-rest from swift

[petea]

@lilpit thanks for spotting this, we'll have a fix in the next release.