http2: fix format argument warnings in tests

Fix two format argument warnings found by vet.

Change-Id: I01d55197c110c2a7486b1bd5dbd0afd74812e535
Reviewed-on: https://go-review.googlesource.com/48090
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

http2/ciphers_test.go

@@ -9,7 +9,7 @@ import "testing"
 func TestIsBadCipherBad(t *testing.T) {
 	for _, c := range badCiphers {
 		if !isBadCipher(c) {
-			t.Errorf("Wrong result for isBadCipher(%d), want true")
+			t.Errorf("Wrong result for isBadCipher(%d), want true", c)
 		}
 	}
 }

http2/server_test.go

@@ -286,7 +286,7 @@ func (st *serverTester) greetAndCheckSettings(checkSetting func(s Setting) error
 
 		case *WindowUpdateFrame:
 			if f.FrameHeader.StreamID != 0 {
-				st.t.Fatalf("WindowUpdate StreamID = %d; want 0", f.FrameHeader.StreamID, 0)
+				st.t.Fatalf("WindowUpdate StreamID = %d; want 0", f.FrameHeader.StreamID)
 			}
 			incr := uint32((&Server{}).initialConnRecvWindowSize() - initialWindowSize)
 			if f.Increment != incr {