fix test error

_cmptest/sha256demo/sha256.go

@@ -3,9 +3,12 @@ package main
 import (
 	"crypto/sha256"
 	"fmt"
+	"io"
 )
 
 func main() {
-	sum := sha256.Sum256([]byte("hello world\n"))
-	fmt.Printf("%x", sum)
+	h := sha256.New()
+	io.WriteString(h, "The fog is getting thicker!")
+	io.WriteString(h, "And Leon's getting laaarger!")
+	fmt.Printf("%x", h.Sum(nil))
 }