message: js: Use substr instead of substring
  This saves 4 bytes from .js.gz and is slightly shorter.
diff: @@ -32,7 +32,7 @@ var MeshoptDecoder = (function() {
  function unhex(data) {
  var bytes = new Uint8Array(data.length / 2);
  for (var i = 0; i < data.length; i += 2) {
  - bytes[i / 2] = parseInt(data.substring(i, i + 2), 16);
  + bytes[i / 2] = parseInt(data.substr(i, 2), 16);
  }
  return bytes.buffer;
  }
  