vmhd should have flags value of 1

The flags byte sequence should always be 0x00 00 01 for vmhd boxes.

@@ -122,7 +122,7 @@ DataView = window.DataView;
   STTS = STCO;
   VMHD = new Uint8Array([
     0x00, // version
-    0x00, 0x00, 0x00, // flags
+    0x00, 0x00, 0x01, // flags
     0x00, 0x00, // graphicsmode
     0x00, 0x00,
     0x00, 0x00,

@@ -92,7 +92,7 @@ test('generates a moov', function() {
     type: 'vmhd',
     size: 20,
     version: 0,
-    flags: new Uint8Array([0, 0, 0]),
+    flags: new Uint8Array([0, 0, 1]),
     graphicsmode: 0,
     opcolor: new Uint16Array([0, 0, 0])
   }, minf.boxes[0], 'generates a vhmd');