support latest pkg:build_runner

pkgs/markdown/pubspec.yaml

diff --git a/pkgs/markdown/pubspec.yaml b/pkgs/markdown/pubspec.yaml
index f9611eb..1e13a33 100644
--- a/pkgs/markdown/pubspec.yaml
+++ b/pkgs/markdown/pubspec.yaml
@@ -1,5 +1,5 @@
 name: markdown
-version: 2.0.2
+version: 2.0.3-dev
 
 description: A library for converting markdown to HTML.
 author: Dart Team <misc@dartlang.org>
@@ -16,7 +16,7 @@
   charcode: ^1.1.0
 
 dev_dependencies:
-  build_runner: ^0.9.1
+  build_runner: ^1.0.0
   build_web_compilers: ^0.4.0
   collection: ^1.2.0
   expected_output: ^1.2.1