presenter/github: Improve handling of moved repos.

Use Repositories.Get method to fetch the owner avatar URL, instead of
relying the github owner name. This works better when the repository
has moved, since redirection works on Repositories.Get endpoint.

presenter/github/github.go

@@ -68,12 +68,12 @@ func presentGitHubRepo(ctx context.Context, gh *github.Client, repo *gps.Repo, g
 	}
 
 	// Use the repo owner avatar image.
-	if user, _, err := gh.Users.Get(ctx, ghOwner); err == nil && user.AvatarURL != nil {
-		p.ImageURL = *user.AvatarURL
+	if repo, _, err := gh.Repositories.Get(ctx, ghOwner, ghRepo); err == nil && repo.Owner != nil && repo.Owner.AvatarURL != nil {
+		p.ImageURL = *repo.Owner.AvatarURL
 	} else if rateLimitErr, ok := err.(*github.RateLimitError); ok {
 		setFirstError(p, rateLimitError{rateLimitErr})
 	} else {
-		setFirstError(p, fmt.Errorf("gh.Users.Get: %v", err))
+		setFirstError(p, fmt.Errorf("gh.Repositories.Get: %v", err))
 	}
 
 	return p