Use latest html5lib and csslib

pubspec.yaml

Index: pubspec.yaml
diff --git a/pubspec.yaml b/pubspec.yaml
index e486bd36da9239aea35e1d2417a41e01b7a3c19e..e89fa325742f7ede3b1b352170e3b204f4cfa606 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -2,17 +2,17 @@ name: web_ui
 author: "Web UI Authors <web-ui-dev@dartlang.org>"
 homepage: https://github.com/dart-lang/web-ui
 description: An easy way to build web apps in Dart.
-version: 0.4.1+4
+version: 0.4.1+5
 dependencies:
   args: ">=0.3.5+1"
   analyzer_experimental: ">=0.3.7+6"
   browser: ">=0.3.5+1"
   # Pin html5lib so we don't get unexpected API breaks.
-  html5lib: ">=0.3.3 <0.3.4"
+  html5lib: ">=0.4.0 <0.4.1"
   csslib: ">=0.4.0 <0.4.1"
   logging: ">=0.3.5+1"
   unittest: ">=0.3.5+1"
-  source_maps: ">=0.3.2 <0.3.3"
+  source_maps: ">=0.4.0 <0.4.1"
   # The following are dev dependencies only, they are not needed by users
   # of the web_ui package.
   js: any