message: Make new Parser and Serializer instances
  Fixes Make new Parser and Serializer instances per call to parse,
  parseFragment, and serialize
diff: @@ -356,18 +356,18 @@ function append(parent, node) {
  }
  var parse5 = require('parse5');
  -var parser = new parse5.Parser();
  -var serializer = new parse5.Serializer();
  -
  function parse(text) {
  + var parser = new parse5.Parser();
  return parser.parse(text);
  }
  function parseFragment(text) {
  + var parser = new parse5.Parser();
  return parser.parseFragment(text);
  }
  function serialize(ast) {
  + var serializer = new parse5.Serializer();
  return serializer.serialize(ast);
  }
  