fix #406 14.6 协程和恢复（recover） defer处少一个括号 (#426)

eBook/14.6.md

@@ -10,7 +10,7 @@ func server(workChan <-chan *Work) {
 }
 
 func safelyDo(work *Work) {
-    defer func {
+    defer func() {
         if err := recover(); err != nil {
             log.Printf("Work failed with %s in %v", err, work)
         }