Note that this is an API-breaking change but should have minimal
impact on users of this package due to the nice inference
properties of the Go programming language.
Bumped `libraryVersion` to `2` due to API-breaking change as
discussed in #376.
Fixes#180.
Change-Id: Ib386135e6b8f306d1f54278968c576f3ceccc4e7
Also:
- add PingHook to RepositoriesService
- move ListServiceHooks to Client, since hooks are no longer just for
repos. Leave behind Repositories.ListServiceHooks for backwards
compatibility
Fixes#178