update book code

eBook/exercises/chapter_14/channel_buffer.go

@@ -0,0 +1,21 @@
+package main
+
+import "fmt"
+import "time"
+
+func main() {
+	c := make(chan int, 50)
+	go func() {
+		time.Sleep(15 * 1e9)
+		x := <-c
+		fmt.Println("received", x)
+	}()
+	fmt.Println("sending", 10)
+	c <- 10
+	fmt.Println("sent", 10)
+}
+/* Output:
+sending 10
+sent 10   // prints immediately
+no further output, because main() then stops
+*/