http2: fix style inconsistency in test

Change-Id: I5ee078009033eea6d4b9320de127a270bd3c439c
Reviewed-on: https://go-review.googlesource.com/43471
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

http2/databuffer_test.go

diff --git a/http2/databuffer_test.go b/http2/databuffer_test.go
index 0018130..028e12e 100644
--- a/http2/databuffer_test.go
+++ b/http2/databuffer_test.go
@@ -71,13 +71,13 @@
 func TestDataBufferAllocation(t *testing.T) {
 	writes := [][]byte{
 		bytes.Repeat([]byte("a"), 1*1024-1),
-		[]byte{'a'},
+		[]byte("a"),
 		bytes.Repeat([]byte("b"), 4*1024-1),
-		[]byte{'b'},
+		[]byte("b"),
 		bytes.Repeat([]byte("c"), 8*1024-1),
-		[]byte{'c'},
+		[]byte("c"),
 		bytes.Repeat([]byte("d"), 16*1024-1),
-		[]byte{'d'},
+		[]byte("d"),
 		bytes.Repeat([]byte("e"), 32*1024),
 	}
 	var wantRead bytes.Buffer