Merge remote-tracking branch 'origin/master'

# Conflicts:
#	src/study/day6/practice4.2.go

src/study/day6/practice4.2.go

@@ -36,7 +36,7 @@ func main() {
 			fmt.Println("参数错误，请输入256，384，512")
 			os.Exit(0)
 		}
-		return []byte{0}
+		return nil
 	}
 	fmt.Printf("%T \n%[1]x \n", sha())
 }