Don't fail immediately if errors occur

Errors are sent to a channel, and one goroutine prints them and sets an
error flag.  If an error was seen, we exit with status 1 after all repos
have been fetched.

go/stars/stars.go

	sem := make(chan bool, config.concurrency)
	var wg sync.WaitGroup
	errors := make(chan error, config.concurrency)
	wg.Add(len(stars))
	for _, info := range stars {
		info := info
			fmt.Printf("% 48s - %s\n", info.RepoName, info.Description)
			err := updateRepo(info)
			if err != nil {
				fmt.Println(err)
				os.Exit(1)
				errors <- fmt.Errorf("Fetching %s: %s", info.RepoName, err)
			}
			wg.Done()
		}()
	}
	hadErrors := false
	go func() {
		for err := range errors {
			hadErrors = true
			fmt.Fprintln(os.Stderr, "Error:", err)
		}
	}()
	wg.Wait()
	close(errors)
	if hadErrors {
		os.Exit(1)
	}
}
func updateRepo(info repoInfo) error {