This is a minor issue. It's also trivial to fix if a minor breaking API change is acceptable (IIRC x/build API is not yet stable, please correct if wrong). It's easier to resolve this sooner rather than later, before it has more users.
Most of the identifiers use "GitHub" or "github" (unexported version) spelling, which is correct and consistent:
But 2 identifiers use "Github", which is neither:
func (*Corpus) TrackGithub
They should be renamed to use "GitHub", if possible.