concurrency: use goroutine(too fast)

concurrency/concurrency.go

@@ -6,7 +6,9 @@ func CheckWebsites(wc WebsiteChecker, urls []string) map[string]bool {
 	results := make(map[string]bool)
 
 	for _, url := range urls {
+		go func() {
 			results[url] = wc(url)
+		}()
 	}
 	return results
 }