Move wg.Done in waitgroup worker to defer

Fixes #310

examples/waitgroups/waitgroups.go

@@ -13,14 +13,14 @@ import (
 // Note that a WaitGroup must be passed to functions by
 // pointer.
 func worker(id int, wg *sync.WaitGroup) {
+	// On return, notify the WaitGroup that we're done.
+	defer wg.Done()
+
 	fmt.Printf("Worker %d starting\n", id)
 
 	// Sleep to simulate an expensive task.
 	time.Sleep(time.Second)
 	fmt.Printf("Worker %d done\n", id)
-
-	// Notify the WaitGroup that this worker is done.
-	wg.Done()
 }
 
 func main() {

examples/waitgroups/waitgroups.hash

@@ -1,2 +1,2 @@
-39bbc00ecd87888761d480666e95d8b2c2a2a589
-oBOGrV0n2Y2
+fd77f5122e6df1669c0a2e0d2c4dfbd30631c21f
+7mWXl0yVe6I