Default to hound's token for the API client

Most of the action happens via HoundCi's github token. Defaulting to
Hound's token makes this process simpler, and makes it easier to see
which actions require the signed-in user's token.
The reason I wanted to do is, is to simplify using the `GithubApi` as I find that I need it often when debugging issues. I see your point about using app specific things inside of `lib/`. Though it could be part of the functionality to default to some `ENV` token variable, maybe something like `ENV["GITHUB_TOKEN"]`"?