Merge pull request #560 from yin1999/patch-1

修复示例代码中的`HTTP/1.x`格式错误

src/ch20-01-single-threaded.md

@@ -371,9 +371,9 @@ fn handle_connection(mut stream: TcpStream) {
     // --snip--
 
     let (status_line, filename) = if buffer.starts_with(get) {
-        ("HTTP/1.1 200 OK\r\n\r\n", "hello.html")
+        ("HTTP/1.1 200 OK", "hello.html")
     } else {
-        ("HTTP/1.1 404 NOT FOUND\r\n\r\n", "404.html")
+        ("HTTP/1.1 404 NOT FOUND", "404.html")
     };
 
     let contents = fs::read_to_string(filename).unwrap();