Update README.md (#172)

Unused import: 'package:html/dom.dart'.
diff --git a/README.md b/README.md
index ca847c2..bd60674 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,6 @@
 
 ```dart
 import 'package:html/parser.dart' show parse;
-import 'package:html/dom.dart';
 
 main() {
   var document = parse(